It seems `ui_handler_region_menu/ui_handle_menu_event` doesn't handle
any events other than press/double-click as they return `WM_UI_HANDLER_BREAK`.
`KM_CLICK` event is not possible due to above case. i.e. clicked element
can't be set active inside `ui_handle_view_item_event()`. (Guess `HANDLER_BREAK` also
prevents from looping over keymap to find relevant keyitem pair to invoke the operator?
Didn't check in details). To fix this, add a condition that checks whether button is in
popup menu. If yes, force active the pressed button and keep the popup open.
Pull Request: https://projects.blender.org/blender/blender/pulls/147047
bc5ab4526a