Broken: (2.80 master, last checked on 6d8a945f06e3dfd720de4839d9df67989ce32388 )
Short description of error
Blender stops in interface_layout.c line 733 while calling
BLI_assert(but->func == NULL);
Exact steps for others to reproduce the error
- Run Blender in Debug Mode
- File -> Export -> FBX
The break can be seen instantly. No blend file needed for this.