Hi narim jacksimov,
Please give me additional details about your scenario. Which docking control do you use - RadDock or DockingManager? In addition, I am not sure what is 'this' in the code snippet that you provided. Your additional details will allow me to provide you with the necessary assistance.
I tried a scenario where I changed the Text of the DocumentWindow, but I was not able to reproduce any issues with Q3 2009 SP1:
"My new text"
the Telerik team