This is the first I've heard of this problem. I'm using Winamp 2.0 (I tried 3.0 ages ago when I first started with lyric tagging and it had some strange behaviour) and the 1.30 SYLT plug-in. I have found no problems with the playback although I did wonder why sometimes scrolling is spot on through emphatic and other times they are just slightly out.

I generally 'click-as-you-sing' and then go back and make some fine tuning examples - sometimes having to playback 4 or 5 times.The maximum I find the lyrics out by is about a second but never getting progressively worse through the song.