Hi Antoine,
We were unable to reproduce the reported issue "Button and Toggle Buttons are disabled while using ToolBarManager inside TabItem". We have prepared a sample to put ToolBarManager inside TabItem ("Tab1") and tried to replicate the issue. You can download it from the following link
Sample:
CustomizedToolBarDemo_SampleIf the issue still persists, please get back to us with your issue reproducible sample. This would help us to proceed further.
Regards,
Durga S.