Issue resolved. The antenna did nothing. The Balupunkt rep was right - the phone wiring was screwed up.

For anyone else in the future who plans to install a Blaupunkt:
I saw some posts that said that the shape of the port on the Blaupunkt allows you to plug-and-play with the stock harness. This is not entirely correct. Unlike other aftermarket stereos, you do not need to swap power and ground for the Blaupunkt. However, on socket A on the head unit, pin 2 is Telephone mute, and pin 3 is sub out. On the stock harness, pin 2 is Reverse Lamp signal (huh?) and pin 3 is Telephone mute. Actually, on my harness, pin 3 was not wired at all.

I suppose I could have gotten a Scosche and rewired the entire harness. Instead, I just disconnected the wire on pin 2 of the harness, plugged the harness directly into the head unit, and everything worked fine.
Well, almost everything. The usb port is not compatible with my mp3 player.