This is not a known issue in RadGrid, so we will need to replicate it first in order to track its cause. Can you paste your grid declaration along with any steps that we need to take in order to replicate the problem. Providing a live url should also help.
the Telerik team
Consider using RadControls for ASP.NET AJAX (built on top of the ASP.NET AJAX framework) as a replacement for the Telerik ASP.NET Classic controls, See the product support lifecycle here.