This is a really strange report and I have not seen such inconsistent behavior with the RadToolTipManager control. There have not been any significant changes in the RadToolTip control in the Q3 2012 or Q1 2013 release and at this point I am not sure what the cause for this behavior on your end could be.
What I can advise is that you examine the following demo that shows a similar scenario and explains how and when targets should be added and cleared: http://demos.telerik.com/aspnet-ajax/tooltip/examples/targetcontrolsandajax/defaultcs.aspx?product=tooltip
. Please compare it to your scenario and try to employ th same approach, as it is possible that the targets in your case are not prperly added and cleared, so some old targets remain when they should have been cleared and all the new ones should have been re-added.
This demo uses controls in a template column, yet the same approach can be used for the grid rows themselves.
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