Game freezes when mew appears (but only on darker storyline)

The same thing as the other guy(s) have said:

I started a new game and once it got to the point in the story that Mew chases off Gengar, Gengar fled but Mew stopped moving and I have no control over the character, the music keeps playing however. Refreshing the map doesn't help the situation. My previous save file that I imported into 1.1 appears to be working fine as well.

But then I tried it on a lighter storyline and it works fine!