I just opened this PR https://github.com/FreeCAD/FreeCAD/pull/481 which is fixing these 2 issues:
- Lot of Coin warnings with bad strings content
- Activate only UI Tree Leaf and hide visibility from Compound created to follow STEP assembly tree. This is currently accelerating browsing of the tree, and allows to display colors from parts and described within STEP files.
ps: I still have into the PR some commit which shouldn't be there. When integrated I will totally resync my tree with master as to avoid this and simplify the integration of my upcoming PR.