As a guess, do you have more than 9 frames? If so, zero-padding the filenames of the bimtaps might help ensure they are sorted correctly. e.g. to prevent '11.png' from being ordered before '2.png' you could create '01.png'..'32.png'
  https://stackoverflow.com/questions/339007/how-to-pad-zeroes-to-a-string
Be aware that gif images are limited to 256 colors, so this may lead to artifacts. Sounds like a question for a different forum,