Bug with merged cells

There is a bug with merged cells. In my table consisting of ca 20 rows 3 of them have merged cells (two first columns are merged). When I move a row from one position to another (for example row 10, so that is 5 now. Row 7 was merged), merges fall apart. It seems the same row number remains merged. But after the movement of rows row no 7 is now row no 8. And this row should have merged cells. Not row no 6 (which is no 7 now). It is easy to reproduce – any row movement with some cells merged destroys them completely.