BCC7 chroma key twice in teh one project

Vegas pro 10, BCC 7

Is it possible to have two chroma-keys active at the same time in teh one project.

I have 4 tracks:

track 1 - footage to chroma key with green background
track 2 - background image for keyed track 1

track 3 - footage to chroma key with green background
track 4 - background image for keyed track 2

the video is 1600 x 600 - for project across 2 x 800 x 600 projectors either side of a stage.

The problem is that as soon as I enable the chroma key on track 3/4, it seems to interfere with the keying on track1/2

Should I be able to have two independent tracks, keyed separately in the same project?

Thank you

Yes it is possible. Are you applying the key to individual events or at the track level?