Thanks for the detailed information. Yes, I was able to replicate the described behavior locally, indeed. I have noticed, however, that this happens only in .NET framework 3.5 and only with the version you have specified: 2012.2.607.35.
I have tested the same scenario with version 2012.2.619.35 where no post back is made upon drop-down list closing. Attached is the same I have been tested locally as well as the trial version of the above mentioned internal build. I encourage you to take a look at it and test it at your end.
Let me know how it goes.
the Telerik team
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