In the screenshot below, both traces are of the same signal. I've swapped probes on channel two, to no effect, and verified the channel one waveform appears when probed on channels three and four. So, I hope I've somehow configured channel two to present the odd waveform ("hope," because I suppose the alternative is I've damaged channel 2). Any ideas what might be causing the weird waveform? Thanks.
Never mind. After posting I noticed in the screenshot that channel two is AC coupled while the others are DC. Switching two to DC fixed it.