Bash: redirect loses output

[gerryino]

I got a problem in a bash redirect:

$ femon -H
screen output:

FE: DiBcom 7000PC (DVBT)
status  C YL | signal  57% | snr   0% | ber 2097151 | unc 31 | FE_HAS_LOCK
status  C YL | signal  57% | snr   0% | ber 2097151 | unc 31 | FE_HAS_LOCK

femon -H > dump
'dump' file contains:

FE: DiBcom 7000PC (DVBT)
status  C YL | signal  57% | snr   0% | ber 2097151 | unc 31 | FE_HAS_LOCK
status  C YL | signal  57% | snr   0% | ber 2097151 | unc 31 | FE_HAS_LOCK

femon -H | grep 'signal'
screen output:

status  C YL | signal  57% | snr   0% | ber 2097151 | unc 31 | FE_HAS_LOCK
status  C YL | signal  57% | snr   0% | ber 2097151 | unc 31 | FE_HAS_LOCK

femon -H | grep 'signal' > dump
'dump' file is empty

I just cant' t figure out why.

femon -H > dump
cat dump | grep 'signal' > d2
Works fine