Test case is a 3x3 table with some text entered in each cell, row-wise "a1", "a2", "a3", "b1" ... "c3". I'll use spreadsheet notation for shorthand e.g. a1:b2 meaning the 4 cells a1, b1, a2, b2.
1. Selecting all 9 cells a1:c3, then right-click-merge, results in what looks like a very narrow table frame with 9 lines of text below it listing the "a1" ... "c3" strings. Saving and reloading the .ddb loses the table frame, and opens just the 9 lines of plain text.
2. Selecting the 6 cells in the 2 leftmost columns a1:b3, then right-click-merge, results in a corrupted 2x2 table, where c2 and c3 seem to overwrite on top of each other in the lower-left cell, and the lower-right cell has no text. Saving and reloading the .ddb loses the table entirely, and opens just 9 lines of plain text.
3. Same as #2 above, but first make a copy of the original 3x3 table so that the page has two tables, one below the other. Repeat the steps for the second table, only, then save and reload. Now both tables are lost, and what opens is just 18 lines of text - even though the first table was not edited or changed at all.
Cheers,
Liviu