Applying keys to a ramp shader???
 

For the animation I am currently working on, I need to have some faces of the model go completely transparent at some point. To do so, I have applied a copy of the ramp shader that i used on the model on these faces and added two keys in the timeline by right clicking the transparency and then set key, so that the faces would go from visible to invisible.

This seemed like an easy task at first, but then maya decides to go bezerk on me and when I play the animation in the perspective view or with the playblast, I get some pretty funky results.

1-The transparency keys sometimes inverse, although in the transperency properties from where i had set the keys, it shows the commands I gave it as I would want them to be. Then it decides not to follow them when running the animation. The weird thing is that on rare occasions by just running the animation again and again and again, it sometimes works properly.

2-Another problem i seem to be having with the transperency, is that instead of going from a black transparent shading to a white one, he decides to improvise and chooses the colors cyan for the beginning of the first key which is supposed to be black and then the color red for the second key which i have put to white.

Bottom line, any method that would make the selected faces of an object disappear would be welcomed.

Any help would greatly be appreciated.
Alex