Satellite radio -- without the antenna

So here is my current setup, necessitated by the fact that either my roof-mounted antenna is busted, the cable that connects that antenna to the antenna jack is cranked, or the jack itself is worn out. Whatever the reason, I have been using what is normally a "home" antenna for my tuner, in my truck:


This necessitates placing said antenna in my glove box when I am going to be parked for any appreciable amount of time, so sometimes if I have several minutes stored up in the tuner's memory I will unplug the antenna and keep listening to Howard Stern while I'm coiling the cable up to put it away. That's when I discovered this:


Don't see anything unusual? Let me show you more clearly:


I can receive the satellite radio signal without the antenna being plugged in. That top jack there, labeled "ANT," should have something plugged into it. At first I thought it was just that there was some signal still left, recorded in the tuner's memory, but even after that ran out I was able to rewind, skip forward again, and even change channels. I still thought it was a fluke, so after my appointment and dinner (having taken the tuner with me) I came back about an hour and a half later, tried it again, and it still worked.

These pictures were taken in midtown Sacramento, around 20th and Capitol. I first noticed this phenomenon at 19th and J Street. I was able to drive around midtown and receive a fairly good signal, with an occasional dropout, but serviceable. I checked the signal strength meter and this is a signal only from a terrestrial repeater, not the satellite directly. As soon as I start to leave the downtown/midtown area I completely lose the signal and have to plug in the antenna again.

So what's the deal? Is the terrestrial repeater signal in midtown Sacramento so strong that one doesn't need an external antenna to receive it? Are there special atmospheric conditions that bounce and focus the repeater signal? Has this always been the case but I've just not had occasion to try listening to my tuner without an antenna plugged in? I prefer to think it's just me and that I'm special, but that's less than 100% likely. A quick search of the SIRIUS Backstage Forums yielded no similar experiences.

Anyone have any ideas?