Set `UI_BLOCK_LIST_ITEM` flag for the block this will assign `UI_BUT_LIST_ITEM` flag for tree view label buttons, see: `uiItemL_()` That way `wcol_list_item` is being used for tree view. (see: `widget_state()` / `widget_state_label()` Pull Request: https://projects.blender.org/blender/blender/pulls/126026