Thank you for your question.
Unfortunately, I am not sure I understand the issue you describe. Do you mean that spell check competed message window is not displayed on top of the screen? Or may be the spell checking dialog is positioned behind another window? Could you please also elaborate a little bit more on your scenario, for example, what type of control is spell checked, what spell checking option is in use: WordByWord
Also, I kindly ask you to share the exact version of RadControls for Silverlight
you are using.
The best approach in such cases is to open a new support ticket and attach a demo project that replicates the issue you experience. Once we are able to observe and analyze the issue, we will do our best to provide you with solution.
Looking forward to your reply.
All the best,
the Telerik team