Track VU only on one channel

Multi tracks recording

Today I had a new problem.
I was recording 6 tracks (3 stereo pairs) The VU meter only gave me a reading on channels 1/2 - the other tracks showed no indication that they had a signal (Yes, the green monitor button is active.)
When I started recording, then the meters showed the activity on all 6 channels.
This happen to anyone else?
Is there a new feature I have set wrong?
Thanks,
Bax