That project appears okay, so I copied in the two DLLs and recompiled my project - still an issue (I can see it's using the new DLL as the Menu & RadGrids look different).
I've then used the IE Developer tools, and can see that the style being applied is the same, although the results are different (again on Chrome, they look the same - correct).
So I merged your page into my project - Still worked fine. So i looked into the headers of my page, as to what could cause it.
Finally tracked the issue down. There was some legacy code from a 3rd party (SolpartWebControls) which we used for Menus (SolpartMenu - which we've since replaced with Telerik RadMenu). We'd not removed the old code, just set the visible = false for when we cut over.
I've got rid of them, and it now works.
Strange how it was happy with one version of Telerik, and not another.