The way patching is supposed to work is: You have TGIDs "A" and "B" programmed. The system patches those two together to a new TGID "X". You don't have TGID "X" programmed, and you're scanning in "closed mode" (no wildcard TGRP object enabled). The scanner recognizes the patch and, because you have at least one of the patch members programmed, monitors the new TGID "X" for the duration of the patch.
The PSR-310/410 do not yet support that (as of firmware version 1.1).
EDIT:
More info... in the above scenario, if the two TGIDs were patched to "B", then you'd hear all of the comms - because you have TGID "B" programmed. The scanner would appear to "follow" the patch, but it's only doing so because you have the supergroup ("B") programmed.
On a PSR-500/600 with firmware 1.8 or later, you'll see that it's following the patch because the "TGRP" text in the upper-right corner of the display will alternate with "ptch".