Reason: I had to make the "BUT" type in Blender to use callbacks *after* the uiBlock was freed, because in Blender several of these callbacks invoke drawing, which isn't possible while a block is being evaluated.
Reason: I had to make the "BUT" type in Blender to use callbacks *after* the uiBlock was freed, because in Blender several of these callbacks invoke drawing, which isn't possible while a block is being evaluated.