- Create a blank new model and select PartDesign WB
- Add a new Body (activated)
- Add a Datum Plane and map it to XY plane
- Select the Datum Plane in the tree view and open its Attachment Offset dialog from the Data property panel
- Check the "Use center of mass" option => Notice the crazy numbers in X & Y fields of Center !!!
- Check the "Apply incremental changes" option => The Center fields are reset to 0
- Change the Angle in the Rotation group => Datum Plane disappeared from the screen
- Validate the task with "OK" then look at the attachment position in the property panel => Crazy numbers again !!
Thanks for confirming.
OS: Ubuntu 18.04.2 LTS (KDE/plasma)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19. <= 2019/07/08
Build type: Release
Python version: 3.6.8
Qt version: 5.9.5
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: French/France (fr_FR)