I agree with the other answers. On rare occasions, TO-xxx packages have bizarre pinouts, but the 78xx series does, in fact, have ground on the middle terminal. This is surely a split power supply in your breadboard power busses, or else a bad breadboard. Many breadboards have splits in the power rails halfway down. I've also seen some with splits more often than that, perhaps as much as disconnects every 5 (or 5 pairs of) contacts. I have a breadboard, for example, which allows for 6 different voltages, all in a single line, from various connections to a battery pack. I'd recommend buzzing the breadboard before starting to use it.
I've also had breadboards whose contacts fail after using larger AWG wires in particular holes (or forcing odd connections, such as machined contacts on IC's or sockets, or larger stamped rectangular pins on a TO package such as this) into breadboard holes. The last thing you want to worry about when building a prototype of a new design is whether or not the wiring under the breadboard works.
Many multimeters have a continuity test capability for diagnosing problems such as these, BUT make sure no power is connected (or you could damage the meter on this setting).