if composite is enabled and and I horizontal scroll(two finger) over the titlebar I can change the transparency of this window. Is this a wanted behavior? because its nowhere documented.
Yes, that's on purpose. two finger scrolling is mouse wheel emulation.
You'd need to press Alt (or whatever key was configured in wm-tweaks settings) though.
Ah no, you right, horizontal scrolling without modifier as well (forgot about that, I added it in 2006).