I'm surprised this was marked as Confirmed.
Looking back on it now I'm fairly sure that you must have camera 0 synced in order to see anything on screen so a better version of
coolgames original snippet would be
sync on
sync rate 60
autocam off
make camera 1
make camera 2
` set the camera backdrops so we can see easily which cameras are being rendered
color backdrop 0, rgb(255, 0, 0) ` red for camera 0
color backdrop 1, rgb(0, 255, 0) ` green for camera 1
color backdrop 2, rgb(255,255,0) ` yellow for camera 2
position camera 0,0,-40
position camera 1,0,0,-40
position camera 2,0,0,-40
point camera 0,0,-80 ` point camera 0 away from the scene objects
point camera 1,0,0,0
point camera 2,0,0,0
set camera view 0, 0, 0, screen width(), screen height()
set camera view 1,0,0,screen width()/2,screen height()
set camera view 2,screen width()/2,0,screen width(),screen height()
make object cube 1,10
set current camera 0
`sync mask 1 ` renders only camera 0 (you should just get a red screen)
`sync mask 1 + 2 ` renders only cameras 0 and 1 (you should see camera 1's output on the left)
`sync mask 1 + 4 ` renders only cameras 0 and 2 (you should see camera 2's output on the right)
sync mask 1 + 2 + 4 ` renders all three cameras (you should see the output from cameras 1 and 2 - this is also the default behaviour)
do
sync
loop
That code works perfectly for me (U77).
So in my opinion this bug should be marked as Fixed or Rejected but certainly not confirmed.