What's the function of the TH headers? (breaks row-/colspan)

When using both row- and colspan simultaneously, that th row breaks the layout. (see attached file and proposed fix)

The thing is - I don’t know what function that thing serves and whether anything possibly gets broken by applying display:none to it.

And for a proper fix, I guess there should never be a rowspan in that th row in the first place?
05_pro_grid_spanheader.zip (1.76 KB)

Unfortunately the usage of the rowspan and colspan for a single cell is not available. Such scenario is not supported.