This seems to be related to This Bug for Windows versions.
I am using WinAmp 1.2.12 and have the pro version, too. I have a Samsung Galaxy S2 with Android ICS 4.0.3. It's an official (stock) ROM. Whilst playing (for example) A file like this one
(Don't worry, the song is freely available; the artist (Haywyre) released the song for free,) Winamp starts out at ~8% of CPU, but slowly creeps up all the way to 50%
Since I have a dual core 1.2GHz phone, that's a lot of CPU resources. The phone stays responsive but winamp does not. I'd press the pause button, and winamp would tell me it'd paused the song, but it just keeps playing. The previous/next buttons do nothing either. Skipping parts / moving the slider does nothing either.
I am unable to play any songs after this (they never start playing) so anytime after playing an m4a file, I have to restart winamp by closing it using the task manager and then opening it again. Naturally I could just convert the files to MP3, but I want to listen to the files as the artist released them, without any converting.
The weird part is that Lossless .wav files which are much bigger play just fine.