[Bug]The col number is wrong when merge all columns and rows to a cell

[kagol]

Insert a 3X3 table and merge all columns and row to a cell, the column number of top column control bar is wrong(expect 1 but 3):

[soccerloway]

The top column control will not merge into one when the cells were merged. I think it is not a necessary feature. The number of top column controls means the max of columns or the number of col tags.