Table Cell Merge Problem

I hope someone can advise of a workaround for this.

I created a new table and then vertically split the first cell. Then I click the first cell again and merged down. I would expect the table to return to its previous layout, but it changes into two rows with four cells in the first row and two cells in the row below. This can be recreated http://ckeditor.com/demo

Please help.
Nitesh