Last edit for a post not showed if no reason given

When someone edit a post without giving any reason, the post is edited but there isn't any "last edit by ...".
If i edit the post again and give a reason, the text is displayed and the edit count is set to 1.
If i edit once again the post without giving a reason, the text is editted and the edit count is set to 2, the message "last edit by..." is displayed.

So the problem is that when no reason is given, on database, post_edit_count and post_edit_user and post_edit_time equals 0,