Please see the following Forum topic and attached images:

http://www.telerik.com/forums/multi-row-tabs#i-uWt1OdnEKceUHt32s43Q

We would consider this to be a bug, and the response we received back from Ivan Danchev was less than satisfactory given that this topic is now over 5 years old.

Please consider adding this to your roadmap and addressing this behaviour sometime in the near future.