A filter's popup doesn't show up when selecting part of merged cells

Steps to Reproduce

1. load the attached file
2. click the row heading at row 2 to select the whole row
2. activate the filter
3. select A1:A2
4. click filter dropdown at A2

Current Result

no dropdown appears

Expected Result

the dropdown shows

Debug Information

1. When the bug happens, if you click another non-selected cell's dropdown, it will show.
2. if you select row 1 or select A1:K2, this bug doesn't happen