Lack of a DOCTYPE at the top of my html was causing IE to render in “quirks” mode which caused the headings to be pushed down.
However, the grab handles to resize the columns are still in the wrong place. I think this has to do with the fact that some columns are hidden.
When all columns are shown, they are in the right place, but as columns are hidden and the existing ones expand, the grab handle still stays in the same/old place.