Usually Ctrl+C copies the operator name to the clipboard
["bpy.ops.material.new()", "bpy.ops.object.material_slot_remove()"]
Crash happens for all buttons of UI_BTYPE_BUT without associated
operator [some are defined with callbacks only, often these are created
with e.g uiDefIconBut (instead of e.g. uiDefIconButO)]

Other examples that crash with Ctrl+C:

• animation decorators next to animatable properties
• button to show a modifier texture in the texture tab
• ...

2.79 survived here (havent checked code, but result in the clipboard was
just not changed hitting Ctrl+C on these buttons), this is what happens
with this patch as well.