(Build 1269)
So it's a bit hard to work out exactly what's going on with this one, but I think the crux of it is that when grouping objects it seems that the group is always sent to layer 0 (even when the grouped objects are initially all in the same layer).
If Layer 0 is hidden then the newly grouped object disappears from view ... in which case I can re-enable Layer 0 and re-assign the grouped object back to the original Layer, however if Layer 0 is visible, then it's not immediately apparent that the Layer has changed.
I understand that when the objects being grouped are individually in different layers before grouping, then the only logical decision I guess is to put the group in Layer 0, however when they're all already in the same Layer, then perhaps it is more appropriate for the group to remain in that Layer.
This opinion is based upon the way that I work --- I tend to use Layers to group multiple objects which are used to compose an assembly or assemblies, but I often need to temporarily un-group assemblies to make changes to individual elements, and then re-group the assembly or assemblies, at which point the assembly and it's components gets re-assigned to Layer 0 (and this fact often goes un-noticed by me if Layer 0 is also visible.)
I imagine that if I was to make changes in all Layers and forget to re-assign the Layer on every occasion after re-grouping, then eventually everything would just end in Layer 0 ... so I think you can see the problem.
As I can have multiple assemblies which I may want to view and work upon independently, I tend to organize each assembly and it's components into it's own Layer. I then want it to remain in this Layer unless I choose to move it elsewhere. The constant re-assignment to Layer 0 causes a bit of chaos which affects my workflow.
Other people may have a different opinion about this if they perhaps use Layers in a different way to me, but this is how it affects my workflow.
CC
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Version 1.0 Bugs and Suggestions