Hello Kevin Schneider,
We are aware of this problem and it will be fixed in the next release of RadControls for ASP.NET AJAX. Basically, this behaviour is manifested whenever a skinned button is put inside a hidden element, and is caused by the inherited display: none of the parent, i.e. it's computed width and height are null.
However, there is a reliable temporary solution. You may find it on that page - http://www.telerik.com/support/kb/article/b454K-hhd-b454T-a-b454c-cbetemdget.aspx
All the best,
the Telerik team