In localizing your demo code for a RichTextBox I noticed some size mode-related inconsistencies in icon placements in the various sorts of buttons:
In Size=large, generally the icon appears above the button text. In the split button the icon is centered over and partially obscures the text. Unacceptable!
In Size=medium, generally the icon appears to the left of the text. In the Split button it appears below the text. Either is fine but should be consistent.
Also, when Size=medium and icon beside text, in all buttons I would like to see more spacing between the icon and the text; there seems to be virtually none.