2b09062def
Previously, the "layers_used" value was getting updated by the drawing code. However, when using copy on write, the drawing code gets evaluated copies of the armature data instead of the original data, so any updates here fail to get flushed to the original data, hence the lack of updates in the UI. Fixed by moving the calculation to RNA when setting bone layers, as it should have been done originally. (The one downside to this is if we set individual layer memberships one by one - this could be slower as the recalc would have to happen each time this changes).