Latest Lame alpha (lame-20011007 confirmed could be other versions as well) has a small quite harmless (from quality point of view) bug.
Athtype 4 seems to actually give the same ath curve as the higher quality athtype 2.
So, for example dm-preset standard (uses athtype 4) and xtreme (uses athtype 2) give identical output with the latest Lame alpha. Both standard and xtreme -profiles give actually xterme profiles's output.
I believe this will be fixed soon.