Could also be as simple as the hieghts of the dunlop and michelins are different. If I had to guess the michelin may have slightly raised the front which could cause the stability issue. Maybe most noticable at higher speed. The michelin probably has a more angular profile, giving you a smaller contact patch when straight up. Without measuring before and after, it's just a guess. Maybe try raising the forks a few milimeters and test riding? It absolutely could be a tire manufacturing issue also.