track matte problems in PPRO2

hi anybody here knows how to fix this problem:

track matte in PPRO2 won't work when i use 3 video layers. it works ok if i only use two layers and as long as i place the files on track 1 and track 2 respectively. if i move the files onto other video tracks, the track matte key won't work anymore and i do change the settings in the pulldown menu.

i've reinstalled premiere hoping to fix the problem but to no avail. this method of keying works perfectly fine on my old pc. Sad

anybody got ideas?