Fade in/out not smooth

Hey.

I got a little problem with Fading pics. I use a lot of those, its fast and easy and often enough for what i´m doing. The problem is when i tween a jpg from 0 to 100 Alpha, then fade it out and fade another one in, I see a unplesent glitch somewhere along the tween.

Is there something i can do about it, something i need to know? My client doesn´t really mind it, but it kind of sucks. Especially seeing the smoothnes of some of the sites out there.

Any advice appreciated. Thanks.