If I tap the B button less than 6 times no lag occurs at all. OR if it does, its very un-noticable. If I tap it more than that then, the entire game goes in slo- mode. And yes, its noticable when the very is VERY VERY VERY active with a screen full of BOMBS covering the entire screen. BUT Again, you can see the frame speed loss slightly if the button is not being pressed like a maniac.
I don't think your GP32 is broken, If your lag continues....try fresh brand new high output batteries. I use NimH batteries. When I use fresh it seems to run smoother(tomak).