ok nevermind …thats odd somehow the glitch does not happen anymore …anyways heres a explanation on how i encountered it yesterday :
[details=Summary]So basically ; place the default particle emitter inside a default part and set the particle emitters drag value to -2 .
Now rotate the camera a bit around and you might notice that sometimes ; suddenly ; and from an specific angle the part somehow turns invisible -> while the part still has transparency 0 ; same for the particles.
It also then rarely looks like the particles would clip trough and or behind the part when rotating the camera quickly enough.
I didnt tested yet if this optical glitch is only visible in studio or also ingame .
BTW : the part gets visible again when changing camera angle and also its color and or transparency ; the glitch also does not work with meshparts as far as i can tell.[/details]