Freezing PFD/ND (747)

Hello, I have an issue where the capt. PFD/ND in the VC freezes, usually on approach. The standby instruments do not freeze nor does anything else. The last time this happened was on approach to KDTW, I was at 3000 and inbound to intercept the localizer for 04R. Just as the a/c started to turn right to intercept the displays froze. The autopilot held the a/c in a 15 degree right bank and began to climb. I disconnected the ap and a few seconds after leveling off the displays returned to normal. The entire incident was approx 25-30 seconds. Any help would be greatly appreciated.Thanks, Steve Marsh