So, to avoid confusion - I was changing multiple things at once. Even though I was sure I'd plugged everything in correctly, I had the head and one of the legs swapped, which I think was the actual cause of the short movement. I changed programmers at the same time I fixed that, hence my confusion.
I was using the USB uploader (as opposed to an AVR programmer), so which programmer is selected in Arduino shouldn't affect things - if it programs successful, I think it should be fine. But there's no harm in making sure it's set to USBtinyISP