Unfortunately it's an issue with the in_mp3 plug-in & how it reacts to output plug-ins reporting low latency vs how it's trying to deal with streams.
I don't have a solution for now (as the in_mp3 plug-in will eventually be replaced with a WACUP built one instead of re-using Winamp 5.666's) other than possibly changing to use a different output plug-in.
-dro