Thanks for your quick response!
Based on your suggestion I've set SmallToNormalThreshold and NormalToSmallThreshold to 200,0 but that hasn't made any difference. The strange thing is that it only affect one tile and all the rest of the tiles are fine.
Can we use Minifier while using Telerik Trial version?
On a side note (being a Silverlight controls vendor) do you have any timescales from Microsoft about this issue http://forums.silverlight.net/forums/t/171739.aspx