If you need to align the content of a GridViewCell in edit-mode, you have to edit its template and set the VerticalAlignment property of the PART_ContentPresenter to Top in this particular state (please refer to the attached picture).
Also you may find attached sample project that demonstrates this approach.
the Telerik team
Registration for Q1 2011 What’s New Webinar Week is now open. Mark your calendar for the week starting March 21st and book your seat
for a walk through all the exciting stuff we ship with the new release!