Merging a top-header cell with an empty cell below it leads to misaligned/incorrectly rendered tables

Issue Summary

Confluence 7.10 onwards, merging a top-header cell with an empty cell underneath it:

• displays correctly during the create/edit-page stage, but
• the merged cells get truncated, and the neighboring (non-empty) cell moves under the merged cell in a last-second post-render change when published.

Steps to Reproduce

1. Create page > insert table > 2x2 layout
2. Create a table like so:

   header1 (merged with an empty cell under me)	header2
   <leave this cell empty>	I am originally under header2 during edit. ←next to me was an empty cell

NOTE: Top row must be headers.

1. Merge header1 with the empty cell underneath
2. Publish page

Expected Results

Merged cells to retain layout that is seen during edit:

Actual Results

Merged cells get truncated, cells at the end of the row shift left:

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available