The current implementation doesn't work when we set the button with a size that is greater than the size of bitmap.
Likely it isn't easy to test this automatically, attached is the testcase I wrote for it.
And this is the comparison: ![comctl32_toolbar_button_bitmap](/uploads/427448b2aaaac1f03feca1eed2fe4bb9/comctl32_toolbar_button_bitmap.png) [toolbar_button_bitmap_testcase.tar.gz](/uploads/51b3018645f7aa46d444cd8d696716e1/toolbar_button_bitmap_testcase.tar.gz)