I wanted to put the Undo and Redo button on my MIDI toolbar (in my own, unpublished, theme).
The .png files are 90x30 pixels; each button is actually 28x28 with a boundary of transparent pixels. They look correct in the Main toolbar. I have both "Don't scale" preferences set, so they are always the same size.
When I use them in the MIDI Editor toolbar, the image is rendered as 29 pixels high - have a look at the lower Undo button in the magnified screenshot. To get them to be displayed correctly I had to change them to be 92x32 and add pink corners - as I have done for the lower Redo button.
BUT, I did not have to do this for the other buttons, e.g. the Snap to Grid button which is 90x30, no pink, in both toolbars.
Has anybody got any idea what I've got wrong?