Dear Support!
In the rtf editor undo of combine cells or split cells does not work in the first row of a table.
It can be reproduced in the wptools demo exe by the steps:
1. create a table (e.g. a 4x4 table)
2. Split a cell in the first row or combine two cells in the first row
3. press Ctrl+Z
In the other rows these operations can be undo, just in the first row cannot.