It's been driving me mad for years but never seen it mentioned.
If I type too much text into a button it expands. If I'm not happy about the size increase and decide to reduce the text an undo takes the text to what it was but leaves the button still expanded.
This has been around for several versions of FileMaker Pro, and our Development and Software Quality Assurance (Testing) departments are aware of this issue. I have made an inquiry to them for an explanation.