I recently gave some people a plugin I was working on and someone reported some errors in the interface.
This is what it's supposed to look like.
You can see that some of the buttons have been pushed down and some are off menu. The one slider is overlapping another button as well. The buttons that seem affected are ones that have fixed widths (which are almost all of them). Their monitor resolution is 1680*1050 so I didn't think that would be a problem. I asked them if they had some custom interface and they told me they didn't. I am not quite sure what the issue is and I am not really sure how to fix it.
The reason is that they have their button size (Preferences>Interface>Button Size) set to a different setting to yours. This affects how the buttons display.
When coding for plugins it is best to use proportional values for button height and width, rather than actual pixels (so 0.5 for half palette, 0.25 for quarter palette, 1 for whole palette, etc.). This means that your layout will remain as you intend (though it is still worth testing at smaller button widths to check that your button names are still sufficiently readable.)