I think there indeed something wrong with "fade-in/fadeouts" happens when JIT is used as ClassicHasClass found before. I found some games which with dynamic core enabled suffer from slow fade in/fade out, but when using "normal" it's more or less ok:
1). Mortal Kombat 3: issue happens not all the time, but most of the time when finish round and things should fade down. Sometimes it abnormally slow.
2). Fallout: all fade in/fade-outs in the whole game is slow. Cpu usage has not risen much, it is like something else make be slow.
With Fallout, it was very hard to check with core=normal, as without jit it pains on loading, but with Mortal Kombat 3 it was easy reproducible (because without JIT on 2ghz CPU its more or less fast as well). And so, when i didn't use JIT after round end, i always have fast fade out. When i use just, then sometime it ok, but most of time its like with micros-pauses. Like pause, then a few frames ok, then again pause. And that pause can be as fast as well as long enough. For example in the fallout, its probably a 1-second pause, and happens 4-5 pauses during fade in/fade out with Jit. With mortal kombat 3 it the same, but sometimes it can even be stuck and nothing happens. In very rare cases I even need to restart DOSBox.
And I can see that on a moment of those slow fade out/fade-ins, CPU loading are 100% (while in whole game about 50-60 while you play).