The problem is indeed strange and I am not able to replicate it locally. Can you please check whether the same issue appear when you move the RadTextBox instance outside of the RadToolBar template (either directly on the page or inside ItemTemplate of other data-bound control)? Additionaly, does this issue appear under a particular browser only or is cross-browser?
The answers to these questions will help us determine whether the issue is related to the toobar instance and how to proceed in our investigation. A live url where the discrepancy can be observed will be appreciated as well.
the Telerik team