Columns width reseted when a fixed header appears

mcmimik

I have a table with merged cells in the header (rowspan, colspan).
When I scroll down, width of some columns is reset.

Example: https://jsbin.com/woxojok/6/edit?output

I think the cause of this bug is rowspan or colspan.

When I try to fix header on the more complicated tables with a lot of sub-columns (like Views), it looks like a mess.

Will be extremely grateful for any workarounds or fixing the bug