A CRJ-700's FGC attempted to capture the PDX 28L ILS early. The flight director commanded a turn in the wrong direction to track the localizer. The crew was hand flying the approach having seen this event occur previously.

Narrative

It's not the autopilot. The First Officer and I were discussing the 'capture problem' that exists when the FGC tries to lock on early to the PDX ILS Runway 28L. After I described the symptoms; he said that he had seen it happen once; didn't understand what had gone wrong; and couldn't get the Captain he was with to believe that it was the avionics; and not him; that had caused the airplane to turn away from the airport when it should be turning inbound. I explained further that the manufacturer thinks that one possible cause might be the autopilot. So he says; 'Mind if I try it raw data; no autopilot?' I said sure; so we did. The conditions were: a clear day; 20 minutes before sundown. ATC gave us 'direct to HANAH; cross at or above 2500 FT; cleared for the visual to Runway 28L.' This gave us an intercept heading of 350 degrees. The autopilot is off; the command bars are removed. He's got raw data and he's hand flying. We have four miles to go to get to the extended centerline. He says; 'push NAV' What should happen in the FMA is to see heading in green (active) and LOC in white (armed). Instead; we instantly got LOC in green. That's bad; but it got worse. When the command bars came up; they commanded a five-degree bank to the left for five seconds; then gradually worked toward a twenty-degree bank to the right -- a turn in the wrong direction. During all of this; the localizer needle never came off the peg; since we still had not reached the centerline. Summing up: an early capture; a turn in the wrong direction; while hand flying. I don't know what's causing this; but it's not the autopilot.