I cannot tell you what might cause the problem because the only thing I can think of is that there is some parent element which does not have explicit size set and you confirm that this is not the case. The only thing I can suggest is that you start applying the same setting you have applied to the grid in your original demo one by one and find out which of them causes the issue. If the problem is not in grid's setting, try putting the parent or child elements one by one until you reproduce the error. Do the same for CSS styles. Once you isolate the problem, remove the unneeded markup and send me the demo along with detailed explanations in case you have not fixed it yourself while isolating the issue.
the Telerik team