HC on Server: Tables look broken when the heading rows contain merged cells

Steps to reproduce:

  1. In a space with Viewport using Help Center theme

  2. Create a page with a table

  3. Set two rows of the table as heading rows → not possible on Cloud, instead: Check ‘header row’ under ‘table options’

  4. Merge two cells from the heading rows which are one on top of the other

  5. Open in Viewport

Expected result:
Table appears correct in Viewport

Actual result:
The second heading row appears shifted in the location where the merged cell was located

Header row 1, cell 1

merged with Row 2, cell 1

Header row 1, cell 2

Header row 1, cell 3

Row 2, cell 2

Row 2, cell 3

Normal cell

Normal cell

Normal cell

Normal cell

Normal cell

Normal cell