Created attachment 161233 [details] patch
It appears that cron has always had its own idea of how long a username can be, it's just been exposed by [r243023]. crontab truncates the tab filename to the first 19 characters and cron complains about orphans. The fix is trivial.
Has been fixed in r305269
I'm sorry that we missed your PR and patch. Marking as a duplicate of the PR referenced in the commit. *** This bug has been marked as a duplicate of bug 212305 ***