From what I can tell, the maximum number of menu buttons (per page) is 18 in HD/BluRay or 36 for DVD.
There is also a limit of 1GB for all menus.
I replaced my motion menu graphics with a still image, reduced the poster frame buttons to text only and still have corrupted buttons in BluRay.
I'm beginning to think that problems like this are why Adobe dropped Encore from the cloud.
I'm not sure what you mean by corrupted buttons. I assume it is related to getting pixelated subpictures:
Are you seeing these only on burned disks? Can you post a screenshot if you are seeing them in computer playback?
Have you selected rich color highlights? This does not appear to be selected by default. But it is odd that the DVD and preview looks okay.