This has been fixed in the official 0.4.0 upstream release found here: https://github.com/Enselic/recordmydesktop/releases/tag/v0.4.0
In fact, this release fixes the following Debian bugs: #588260 recordmydesktop: There is no --y=N option #706574 recordmydesktop: truncates recordings #649824 recordmydesktop: Specifying --use-jack makes recordmydesktop exit with a bad screen geometry #859686 recordmydesktop: man page is really ugly #584269 recordmydesktop: Typo with recordmydesktop Let me know if I can help in any way to get this Debian package updated.
