grep / zgrep issue

Hello.

I may have found a bug in the zgrep utility.

When I use this command:
p-cleber.baldan@logbox:/usr/local/apache/logs/prelogs/xxxxxxxx$ find .
-name "abc.log.*" | xargs zgrep -E -i -c -l '(CBL discontinuation)'
./abc.log.2014-05-12.gz
./abc.log.2014-05-13.gz


When I use *-c* it works fine.
But when i add *-l* in the same command line with *-c*, the output won't
have the count of results anymore.
I wanted to have the count of occurences per file

Please, let me know if this is not a bug.

Regards,
Cleber.