So I'm breadboarding with a Nano 328. I had D2 set as an input with the internal pull-up on, and was getting some erratic readings, with it returning LOW when it shouldn't. So I probed it with a meter and found that when unconnected to anything else, the voltage from pin to ground was all over the place. I then did the same for the rest of the digital pins. From this, I determined that digital 2, 3, 5, 6, 8 and 9 were behaving oddly, with the remainder behaving normally. I then tested them as outputs, where all except 8 were behaving as normal. D8 was at a constant 2V regardless of what I was writing to it. I then swapped the board for another and found exactly the same problem.
Is this a known behavior for the 328? I'm especially concerned by the pin 8 thing. These aren't official Gravitech boards, but it seems more like a micro issue given that they (mostly) work as outputs.