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 (result in the clipboard was just not changed hitting Ctrl+C on these buttons), this is what happens with this patch as well. Maniphest Tasks: T71405 Differential Revision: https://developer.blender.org/D6208