Problem summary

While adding a new row to a table when there are merged cells present, the new row's merge behavior is inconsistent.

Cell merge type on current row	New row position	Result
Cells merged across columns	Insert above	Cells in new row copies the current row's merges
Cells merged across columns	Insert below	Cells in new row copies the current row's merges
Cells merged across rows	Insert above	Cells in new row does not extend the current row's merged cells
Cells merged across rows	Insert below	Cells in new row extends the current row's merged cells

The third scenario stands out from the rest as it does not not extend the merged cells, and instead inserts a standalone cell above the merged cells. It appears to duplicate the row formatting from the row above instead of using the current row's formatting.

The fourth scenario inserts a row below, and it does correctly extend the merged cells so that now the merge is one cell longer.