I have 2 line header grid and everything is fine (26px + 26px height) until I want to fix the first column. When I add .enableAutoWidth() and .splitAt() the heights become 36px + 46px and also the vertical positioning looks ugly.
Unfortunately the only solution in this case is to avoid the usage of the rowspan in the first column of your grid
(as a workaround you may add a “fake” first column without a rowspan with “0” width).