there are several pa to md/do folks on this board.
corpsmanup is a pgy-1 in em and a former pa.
bandit is an ms-4
the medical director at pacific university's pa program is a pa turned md internist.
it's fairly common as it is a natural transition. pa's who go to medschool still have to do all 4 yrs as there currently are no bridge programs but it is much easier for them having already done 1/2 of the didactic material and a full yr of rotations equivalent to ms3.