The Peter Principle has struck again! I replaced the steering head bearings and races over the winter. I adjusted the bearings per the directions over at airheads.org. Finally got to ride it today. After about 10 miles, with some progressively harder braking to bead in new pads, the bearings loosened to the point where I now have 1/4 to 1/2 inch of play front to back at the axle. It seemed to happen suddenly, i.e., I suddenly felt the wheel moving back and forth under braking. It was a little disconcerting, but oddly the handling seemed fine in turns at the mild pace I held on the way back home.
I'm guessing one of the races wasn't properly seated and shifted into place under braking load. I'm also guessing I simply need to readjust the bearings and it should be fine, but I'd appreciate any thoughts.