Thank you for writing.
From your question I am guessing that you are doing the things correctly as far as the code is concerned. Perhaps the issue might be from the settings in your theme. Would you please confirm that you are setting the margin for the main state of the element? The way your question sounds seems that you are setting it at the MouseOver
state. If that is the case, please change the settings and the things should be alright.
I am attaching an image which will help you see exactly what I am talking about.
If you confirm that you are setting the margin at the right place, would you send me the tssp file in order to check what might be the problem.
Hope that helps, Please do not hesitate to contact us in case you face other issues.
the Telerik team