Port tack overpowering steering

[enadler]

we have a 2001 40 ft jeanneau, with a 130 jenny and inmast roller main. recently we have run into a puzzling issue, here's the scenarios:

wind is 15-20kts, gusting to 25; starboard tack with full main no headsail crusing along on a close reach at 5 kts holding a straight course with the autopilot. wind drops to a steady 15kts so we unfurl the jenny to its second reef point and continue on a straight course picking up to 6+kts boat speed. Now the issue, we come about to a port tack sails are set the same on a close reach, but now the boat wants to head up into the wind, we have a tough time after taking her off auto keeping her on a straight line. As we head up into the wind, of course itpicks back up to 20+kts, burys the rail and we have a hard time getting her back on course so we roll in the headsail. This has repeated itself on a few occassions, this past weekend we found ourselves struggling against gusts that jumped back to 25+, s now we are hesitant to put out all sails unless the wind is light. Any thoughts as to why the boat wants to head up only on a port tack??

Thanks