If there is a patch between talkgroup X and talkgroup Y, You can hear the patch traffic by monitoring talkgroup X or talkgroup Y. You just can't monitor the patch itself. Try using ID SEARCH instead of ID SCAN.
I tested this on the large 2,600 talkgroup Colorado DTRS P25 phase 1 system using a BCD436HP and it does not work. If I am monitoring one CSP talkgroup (A) and they patch into another CSP talkgroup (B) which is not enabled and which I am not interested in monitoring on a regular basis, then I cease to receive all traffic on talkgroup A.
I also tested this on the Weld County, Colorado FRCC P25 phase 2 system using a BCD436HP and it does not work either. Our dispatch office often patches three police clearance channels together (county {A}, sheriff North {B} and sheriff South {C}). This is clearly seen in the Pro96Com software where B is shown as patched into A and also C is shown as patched into A. The only way to monitor traffic on B or C in a Uniden BCD436HP is if A is enabled. However, on the GRE scanners, a person can have just one of any A or B or C enabled and all the traffic patched together is received. I verified this with a BCD436HP and a PSR-600 running side by side. Avoid A on the Uniden and no further traffic is heard even though B and C are enabled and not avoided. However, temporarily lock out A on the GRE scanner and traffic is still heard from B and C.
Uniden just needs to fix this plain and simple or they are going to fall by the way side sooner or later when a better company comes along that listens to its consumers.
Shawn