With V8.0 the method TRzToolButton.CheckMinSize was changed in a way that makes sure that the button is somewhat larger (8 pixel on 96 dpi) than the image, while before it could as well be the same size as the image. Unfortunately there is no way to configure that padding size nor is CheckMinSize virtual to allow an inherited class to override that behavior.
In my applications I make heavy use of TRzToolButton where the images have to be the same size as the buttons. V8.0 breaks that completely.