In this question, I saved 13 secs after A__, in revision 24. Both I and they deleted ", or is at the end of a line" because they say they will in a comment, and we both also changed something else. My edit overwrites theirs and I didn't get any notifications.
I didn't ask, but this may have happened again in revision 27. I have deleted two spaces in the last minute of the grace period of revision 26. After revision 27, 11 secs after the grace period, the spaces are back.
According to the screenshots, we are supposed to refresh and manually compare what has changed before saving again, which probably won't happen in a few seconds, even if (or especially if) they are just two insignificant spaces.