I hope this has not been mentioned before, I did not find it mentioned in this forum when looking for it.
When you modify your comment and add just a word, or sometimes a small sentence, and then click on Save, you can't do it and instead the message appears:
"The body of the message has been left empty" and that's regardless of how long your message actually is.
And then I somehow try to work around it by cutting out and re-pasting passages, or writing some random stuff and then deleting it,and then sometimes it works.
Or sometimes I go back and click on the modify button of the comment again, and the second time it might work better.
It's not really reliable and doesn't always work when you do small editings.