If group and object has same prefix, then when putting object into this group, or pulling out, object may dissapear
After close / open project, dissapeared object will be on place before grouping operation, even if project was saved after object disappearing.
This affect all type of objects, but only when group name and object name has same prefix.
Example in attachement. Try to pull out or drop into group.
OS: Ubuntu 18.04.4 LTS (Unity:Unity7:ubuntu/unity)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Build type: Release
Python version: 3.6.9
Qt version: 5.9.5
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: Russian/Russia (ru_RU)