How to reproduce:
1. Click a cell
2. Type "ret 2" (without quotes)
3. Press Enter
4. See the text changed to "Ret 2"
5. Press Ctrl+Z (which, as a user would think, should undo the autocorrection)
6. See text removed
The expected result in (6.) is that the text changed to "ret 2" instead of being removed.
A workaround to this is (if not disabling autocorrect completely) to cut the required (i.e. not autocorrected) text to clipboard from the cell, press Enter, then click again on the cell and press Ctrl+V.
already known issue
*** This bug has been marked as a duplicate of bug 79404 ***