Two mut Managed Boxes Vectors ++ error

fn main() {
let mut your_favorite_numbers = @[1,2,3];
let  my_favorite_numbers = @[4,5,6];
let  f = your_favorite_numbers + my_favorite_numbers;
println(fmt!("The third favorite number is %?.", f))

}
it will out put The third favorite number is @[1, 2, 3, 4, 5, 6].
but when change: let f = my_favorite_numbers + your_favorite_numbers;
here's an internal compiler error.like
error: internal compiler error: no enclosing scope with id 33

use core::io::println;

fn main() {
    let  mut your_favorite_numbers = @[1,2,3];
    let  mut my_favorite_numbers = @[4,5,6];
    let  f = your_favorite_numbers + my_favorite_numbers;
    println(fmt!("The third favorite number is %?.", f))
}

the compiler give the same error

long message

/usr/local/bin/../lib/librustrt.so(_ZN9rust_task13begin_failureEPKcS1_m+0x4b)[0x7fbb1ca57cfb]
/usr/local/bin/../lib/librustrt.so(+0x2aae9)[0x7fbb1ca68ae9]
/usr/local/bin/../lib/librustrt.so(upcall_fail+0x1a8)[0x7fbb1ca59ae8]
/usr/local/bin/../lib/libcore-c3ca5d77d81b46c1-0.7-pre.so(+0x10a81b)[0x7fbb1e64481b]
/usr/local/bin/../lib/libcore-c3ca5d77d81b46c1-0.7-pre.so(+0x10a7c2)[0x7fbb1e6447c2]
/usr/local/bin/../lib/libcore-c3ca5d77d81b46c1-0.7-pre.so(_ZN3sys12begin_unwind17_61fe198059b9e3fc6_07preE+0x71)[0x7fbb1e589db1]
/usr/local/bin/../lib/libsyntax-84efebcb12c867a2-0.7-pre.so(_ZN10diagnostic14__extensions__9meth_87425fatal15_c79235bb6437b76_07preE+0x177)[0x7fbb1da95d27]
/usr/local/bin/../lib/libsyntax-84efebcb12c867a2-0.7-pre.so(_ZN10diagnostic14__extensions__9meth_87653bug15_c79235bb6437b76_07preE+0x6f)[0x7fbb1da964bf]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(_ZN6driver7session14__extensions__10meth_194963bug17_b5f71376f9f489aa6_07preE+0x80)[0x7fbb1cdb5f30]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(_ZN6middle5trans4base16add_root_cleanup16_c559fab57337f3c6_07preE+0xb55)[0x7fbb1ce83155]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(_ZN6middle5trans5datum14__extensions__10meth_268174root16_f0b22436e53f4c56_07preE+0x69f)[0x7fbb1ce812af]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(+0x210e17)[0x7fbb1ceabe17]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(+0x20f090)[0x7fbb1ceaa090]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(_ZN6middle5trans4expr14trans_to_datum17_9af25a1c6031ba326_07preE+0x309)[0x7fbb1ce10049]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(_ZN6middle5trans6callee14trans_arg_expr15_88afae98ebb58b6_07preE+0x9d9)[0x7fbb1cea6809]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(+0x8eb804)[0x7fbb1d586804]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(+0x20ad54)[0x7fbb1cea5d54]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(_ZN6middle5trans6callee10trans_args17_cc8c7f6bee1899e26_07preE+0x1d1)[0x7fbb1cea47f1]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(+0x208a38)[0x7fbb1cea3a38]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(_ZN6middle5trans4base10with_scope17_7c2287baeb8678276_07preE+0x56e)[0x7fbb1ce60e0e]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(_ZN6middle5trans6callee16trans_call_inner16_1e7ecf3fc31ec816_07preE+0xc2)[0x7fbb1ce90062]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(+0x222551)[0x7fbb1cebd551]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(+0x2156d1)[0x7fbb1ceb06d1]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(_ZN6middle5trans4expr10trans_into16_6b13b456a33b9916_07preE+0xf14)[0x7fbb1ce0ceb4]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(_ZN6middle5trans4base10init_local16_847eb87a0711c956_07preE+0x64a)[0x7fbb1cf1324a]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(+0x27a50b)[0x7fbb1cf1550b]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(_ZN6middle5trans4base10trans_stmt16_86496c75f98d7dc6_07preE+0x5ae)[0x7fbb1ce0bbbe]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(+0x16fbfc)[0x7fbb1ce0abfc]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(_ZN6middle5trans11controlflow11trans_block16_f8749781b9f86756_07preE+0x19e)[0x7fbb1ce0933e]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(_ZN6middle5trans4base13trans_closure17_b72caf81394456906_07preE+0x744)[0x7fbb1cf1ef34]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(_ZN6middle5trans4base8trans_fn16_e94b12536796af36_07preE+0x536)[0x7fbb1cdbd766]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(_ZN6middle5trans4base10trans_item17_f01c7ec8d27812b16_07preE+0xd71)[0x7fbb1cdb51d1]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(_ZN6middle5trans4base9trans_mod17_5a4ea143b385448e6_07preE+0xa3)[0x7fbb1cf25743]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(_ZN6middle5trans4base11trans_crate17_493b2c14ccd948d06_07preE+0x1477)[0x7fbb1cf474e7]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(+0x8eb804)[0x7fbb1d586804]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(+0x8a8e20)[0x7fbb1d543e20]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(_ZN6driver6driver12compile_rest17_bd8ae2181a50d4676_07preE+0x336a)[0x7fbb1d540e7a]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(+0x8eb804)[0x7fbb1d586804]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(_ZN6driver6driver12compile_upto17_b11eb8cfd0ac14e56_07preE+0x108)[0x7fbb1d544038]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(_ZN6driver6driver13compile_input17_5a75f667ec5941cb6_07preE+0xca)[0x7fbb1d54447a]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(_ZN12run_compiler16_524cd4cee168d5f6_07preE+0x20a0)[0x7fbb1d576dd0]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(+0x8e9191)[0x7fbb1d584191]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(+0x8e561a)[0x7fbb1d58061a]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(+0x8eb804)[0x7fbb1d586804]
/usr/local/bin/../lib/libcore-c3ca5d77d81b46c1-0.7-pre.so(+0xd205f)[0x7fbb1e60c05f]
/usr/local/bin/../lib/libcore-c3ca5d77d81b46c1-0.7-pre.so(+0x154704)[0x7fbb1e68e704]
/usr/local/bin/../lib/librustrt.so(_Z18task_start_wrapperP10spawn_args+0x24)[0x7fbb1ca58544]
rust: task failed at 'explicit failure', /home/resolute/DeveloperTools/rust/src/librustc/rustc.rc:358
/usr/local/bin/../lib/librustrt.so(_ZN9rust_task13begin_failureEPKcS1_m+0x4b)[0x7fbb1ca57cfb]
/usr/local/bin/../lib/librustrt.so(+0x2aae9)[0x7fbb1ca68ae9]
/usr/local/bin/../lib/librustrt.so(upcall_fail+0x1a8)[0x7fbb1ca59ae8]
/usr/local/bin/../lib/libcore-c3ca5d77d81b46c1-0.7-pre.so(+0x10a81b)[0x7fbb1e64481b]
/usr/local/bin/../lib/libcore-c3ca5d77d81b46c1-0.7-pre.so(+0x10a7c2)[0x7fbb1e6447c2]
/usr/local/bin/../lib/libcore-c3ca5d77d81b46c1-0.7-pre.so(_ZN3sys12begin_unwind17_61fe198059b9e3fc6_07preE+0x71)[0x7fbb1e589db1]
/usr/local/bin/../lib/libcore-c3ca5d77d81b46c1-0.7-pre.so(+0x154704)[0x7fbb1e68e704]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(_ZN7monitor16_865e1633f355e1d6_07preE+0x18f7)[0x7fbb1d579737]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(+0x8eb804)[0x7fbb1d586804]
/usr/local/bin/../lib/librustc-c84825241471686d-0.7-pre.so(_ZN4main15_c4de63b748e03d6_07preE+0x7e)[0x7fbb1d58641e]
/usr/local/bin/../lib/librustrt.so(_Z18task_start_wrapperP10spawn_args+0x24)[0x7fbb1ca58544]
rust: domain main @0x1818c20 root task failed

[emberian]

Cannot reproduce; needs testcase.