I would say that it has a lot to do with the fact that one language is visual and the other is auditory/oral, and their syntax, concept, and often pragmatics are different. I find that I can communicate in ASL on a didactic level and never put anything into a voiced English order much easier than I can communicate in ASL, and then interpret into English. I understand sign on a different cognitive level than English, and the process of converting from one cognitive process to another takes a minute or two. Also, because ASL is not word for word sign translation of English, it may nature requires a delay before voicing what has been signed. You must watch the sign long enough to get the concept, then start interpreting, and in the meantime, you are attempting to hold onto what is continuing to be signed. If you start to voice too soon, you will often need to back up and correct a mistake in concept. That appears to be a dysfluency in the voicing.
