why am I asked to delete or post my comment after edits

Sorry yes, I mean pdf files. Here's what's happening when I try to edit a pdf:
1) I make my first edit (e.g. replace a word or delete a word);
2) When I go to make the next edit, the following message pops up (in red font) in the comments window: 'Please cancel or post the comment'.
That message will only disappear if I save the file, which means I currently have to do a save after each and every edit.
[Also, a box is visible near my mouse cursor, which may have nothing to do with the above issue.]