Recent builds can hang with 100% CPU utilization

Several times over the last few days I have caught ntpd soaking up an entire core. Attempting to communicate with ntpq times out, and it is necessary to use -9 when killing the daemon.

I am running Ubuntu MATE 16.04.2 with kernel 4.4.0-78-generic, upgraded from 15.10 (IIRC). I have no idea what triggers this, or how to replicate it. I built from a just pulled HEAD afternoon (IIRC) yesterday and it hung this morning.