I don't know if this is related to what you're talking about or not but on my PSR-800 in Catonsville the HoCo Northern District dispatch will always say that it's on a patch, I've never really thought a thing of it.
That's *probably* a typical "within system" patch of multiple talkgroups. This could be for many reasons -- for example, wanting several talkgroups to be merged so a single dispatcher can handle it, conslidation of districts or barracks, or temporary to transmit a broadcast across multiple talkgroups simultaneously, etc.
The patch I'm talking about results in activity for one jurisdiction being patched onto (from) another neighboring system -- generally because of poor coverage/reception in that specific area (Howard County has poor radio coverage/dead spots in Elkridge but the Anne Arundel system has good coverage in that same area, etc.). In this case, I believe what happens is the Howard unit actually transmits on the Anne Arundel system and Howard County patches that activity back onto the Howard system.