Turns out the problem in my hip seems to be that my left femoral head is not sitting quite properly into its socket; it is slightly posterior of where it belongs. This means that all the surrounding stabilizer muscles are overcompensating, and after six months of working out or so they decided to let me know about it. :) The good news is it should be remedied reasonably easily with exercises to strengthen my core abdominal muscles (already underway with trainer Heidi) and additional exercises focusing on gently improving and realigning the currently strained set of muscles. Oh, and some likely-to-be-uncomfortable medical massage. I'm off the training schedule and set up for twice-weekly PT sessions for the next 4 weeks.
I'm not terribly surprised to find my hip(s) out of alignment - the childhood hip dysplasia I grew up wearing a brace for explains it quite neatly. It's one of those things I've almost been expecting to happen knowing my health history. It shouldn't limit my activities at all once the pain and overuse are remedied. So good news on the whole.