Unexpected behavior of KeepIndex with partitioned axis

[bgctw]

Currently getpropery and getindex using KeepIndex return different values.

Using the example of #41, I expected the result using KeepIndex to return ComponentVector(boids = <LazyArray>) rather than only the first entry.

    boid = ComponentArray(pos=zeros(2), vel=zeros(2))   
    u0 = ComponentArray(boids=repeat([boid], 2))    
    u0.boids
#2-element LazyArray{ComponentVector{Float64, SubArray{Float64, 1, Vector{Float64}, Tuple{UnitRange{Int64}}, true}, Tuple{Axis{(pos = 1:2, vel = 3:4)}}}}:
# ComponentVector{Float64,SubArray...}(pos = [0.0, 0.0], vel = [0.0, 0.0])
# ComponentVector{Float64,SubArray...}(pos = [0.0, 0.0], vel = [0.0, 0.0])

    u0[KeepIndex(:boids)]
# ComponentVector{Float64}(boids = (pos = [0.0, 0.0], vel = [0.0, 0.0]))