It does take a little playing about and time to get used to Xara layers, grouping and soft grouping attributes.. There are countless times when things like this have happened to me and I end up having to examine each bit of the button or menu bar until I see what I did wrong. When creating new buttons and menus I have started to use the Solo mode ALOT more to ensure I am working on individual layers to prevent from getting it wrong and having to fix it.

Not an answer to your question but from experience.