Thank you for the additional details. This helped me to reproduce described content panel behavior when changing tab Name. However, after closing with OK button items editor it seems that everything comes on its place and I have not troubles to use the instance of TabOnline in the code. Nevertheless, we will consider improving this design-time behavior in one of the next releases. I have updated your Telerik points for bringing to this our attention.
Do not hesitate to contact me again if you have any other questions.
the Telerik team