I had the same issue. Turned out that the small arrow that appears to identify that column as the sort column, and the sorting direction, was not correctly positioned vertically. So, the Column heading correctly shifted to the left as if there was a new character on the right. Problem was that I couldn't see the new 'arrow' character since the heading row height was 'clipping' the arrow that was incorrectly positioned on the line below.
Different browsers/resolutions seem to give different results, from seeing none of the arrow to seeing only half of it.
I still haven't solved the issue. :(
My code is not that far from the basic.htm which worked fine. I plan to revert back to it, and make one change a t a time to try and isolate the cause. Haven't had time yet.