When creating Comment you must type in at least one character or the box disappears if you click away from it. Also you cannot resize or move the box. Similar problems occur during Edit Comment.
Seems it works if 'show comment' it's active. I don't know if it is really a bug or it is so by design.
2 issues here. 1st is a result of https://bugs.documentfoundation.org/show_bug.cgi?id=83575 2nd is a duplicate of Bug 68695. Rule of thumb is search before reporting. *** This bug has been marked as a duplicate of bug 68695 ***