strange behaviour when grepping output of tail

[Frits Verlijsdonk]

tail -f /var/log/messages | grep "foo"

above works fine and i get lines with "foo"  that gets into
/var/log/messages.

tail -f /var/log/messages | grep "foo" | grep "bar"

doesn't produce any output although there are lines with "foo" and "bar"

tail -f /var/log/messages | grep "foo" | grep "foo"

This doesn't produce any output either !!!

After breaking the tail command i test wether there were lines that should
have been displayed. Then i see that there were valid lines

cat /var/log/messages | grep "foo" | grep "bar"

I assume it is a bug but i'm not sure

I use Suse linux 6.3 and have installed
tail (GNU textutils) 2.0
grep (GNU grep) 2.4.2

Frits Verlijsdonk
system administrator
Smeva BV, The Netherlands