I do think that this should be rolled back. It feels almost necessary to be able to lay mines while retreating, to hold back enemies while the rest of the defending team are getting set up for the next push.
I think that it might still be possible with SLAMs (same as how the EOD bot can be used to lay mines out of bounds and in enemy HQs), but I need to remember to test in case I imagined that.
Edit: Only had enough time after work for a super quick test, but it might be worth playing around with the SLAMs. I was able to lay them while OOB in the first sector, and could drop them during the retreat too. Wish I'd had the time to remind myself if the regular mines can be dropped OOB, but I'll try to remember to fiddle more.
OOB placement: https://www.xbox.com/play/media/DdLNXcBDek
Retreating: https://www.xbox.com/play/media/kbsUnkg6e3