This is not a known issue, however I've managed to reproduce it using standard ASP.NET CheckBox. The problems seems to show up in the Q1 Service Pack 1 version (This is 2010.1 415). I have checked both Q3 and Q1 and they seem to work okay. Which version did you test? The good news are that with the latest service pack (which was release yesterday) the problem is gone. We suggest that you upgrade to the latest service pack.
If your issue is not resolved in the service pack please paste here your RadListBox declaration as well as the exact item template so that we can research the problem locally.
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