This is known issue that we hit after a fix on FontSize-s we made for RibbonView in Office2013 theme. I logged the issue in our feedback portal where you might track its status - here
is link to it. We'll do our best to fix this for the upcoming service pack or release.
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Feedback Portal
and vote to affect the priority of the items