You have already sorted the document mode. Doesn't this solve the problem? This is usually a trick.
Browser mode should not enter the game, since it does not affect rendering at all; it just changes the UA line, so it should not have any effect on the page layout .... unless there is something in the code that the browser hack is trying to do by looking at the UA line.
If you have something in your code that does this, then where is the problem, and you should probably fix it. (using the UA string to influence the page layout is usually frowned as bad practice anyway, there are usually better ways to do this)
If he does Telerik himself, then I would suggest that they were already forced to find a fix for him (IE10 had not worked for a long time, and they would have other users complaining), so you can update to the latest version to solve the problem.
Spudley
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