meld offers to discard changes in both compared files when the file from only one of the sides changes on disk
I was hand-merging changes from the right side into the left side.
Then I decided to use an external tool to update the right-side file because there were too many changes to be made.
When the right-side file changed on disk meld offered me to discard changes in both left and right sides, despite only the right side has changed on disk.
meld should only offer to discard the changes from the same side of the comparison when the disk changes, because the other side has nothing to do with the disk file change.