Hi Marco ,
It was known bug and fixed for the 2009.1.605.1 internal build of OpenAccess. I guess you are using some older version and that is why you still see the misbehavior. If your case is not to urgent, I would suggest you use the upcoming Q2 release of the OpenAccessDataSource that should really be the most stable version so far.
If you are using the latest version an still have the problem, could you please collaborate a bit with us and describe the problem in more detail, so we could do the fix in time for the Q2 release.
All the best,
the Telerik team