10-14-2017, 10:07 PM
It also happens sporadically to me (Ubuntu 16.04 with KDE). Not that often since the oldest timestamp in my current one goes back to September 2. The only explanation I have is that some application somewhere is mishandling it (and that would be an application I use less often that you do). To list applications that use it:
(of course, if an application breaks it each time it tries to use it, it won't appear in that list).
Code:
grep -ore 'bookmark:application name="[^"]\+' ~/.local/share/recently-used.xbel | sort -u