Yes, this happens often, Milwaukee is often heard on the various 460.xxx freqs, especially when the bands open. CPD officers won't normally hear it as long as the radios are not in the Monitor position due to the different PL. I am sure it occasionally causes some hetrodyne and annoyance though.
Milwaukee FD used to come in on CFD's "Main" repeater (154.130) since they both had th same input channels and Main's repeater had at least one RX site that had no PL. That lasted for a few years and eventually they fixed the issue.
I heard McHenery County on 154.3850 twice today and someone on 154.1300 faint but active. So, that seems like a possibily, however it was faint so I could not get the pl or ctcss.
But my 800 mghz antena is only at 8ft in the air with a base ant convert kit deal. It was somthing I put together so I could hear fd and pd better in my area on in outside antena with out getting up on the roof as opposed to the stock for the 396t. Mix results, the 5/8 3db wave was complete bad, quterwave was a lot better and 800 was the next choice. The base fiberglass antena with 4db gain claimed did about as well as the quterwave. (not surpising as I oppend it as an experminet to see the rod length discovering it resemble that much of a quterwave whip.
At least I now can hear norridge pd again from my handheld scanner, its amazing how much bad rf is in my area and how much poor signal their is.