BUG #12779: pg_dump -Fd doesn't care about -Z

The following bug has been logged on the website:

Bug reference:      12779
Logged by:          Christoph Berg
Email address:      christoph.berg@credativ.de
PostgreSQL version: 9.4.1
Operating system:   Linux (Debian 8)
Description:

pg_dump -Fd doesn't seem to care about -Z for Z > 0:

$ for i in {0..9}; do echo $i; pg_dump -Z$i -Fd -f $i.fd postgres ; done
$ du ?.fd
5392    0.fd
1164    1.fd
1164    2.fd
1164    3.fd
1164    4.fd
1164    5.fd
1164    6.fd
1164    7.fd
1164    8.fd
1164    9.fd

In contrast with -Fc, where it works:

$ for i in {0..9}; do echo $i; pg_dump -Z$i -Fc -f $i.fc postgres ; done
$ du ?.fc
7548    0.fc
1488    1.fc
1440    2.fc
1392    3.fc
1240    4.fc
1148    5.fc
1160    6.fc
1156    7.fc
1160    8.fc
1160    9.fc