git log --summary outputs extra newlines inconsistently

‘git log --summary’ seems to output a newline after every non-merge 
commit.

  $ git log --summary --pretty=format:'%h %s'
  3c0eee3 Linux 2.6.37
  
  65f4288 Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-2.6
  9fc3bbb ipv4/route.c: respect prefsrc for local routes
  
  8a87694 remove trim_fs method from Documentation/filesystems/Locking
  
  989d873 Merge master.kernel.org:/home/rmk/linux-2.6-arm
  d9a1abe arch/mn10300/kernel/irq.c: fix build
  
  867c202 ima: fix add LSM rule bug

  …

Oddly, those newlines show up even with -z!

  $ git log --summary --pretty=format:%h -z
  3c0eee3
  ^@65f4288^@9fc3bbb
  ^@8a87694
  ^@989d873^@d9a1abe
  ^@867c202
  …

This makes the output annoying to parse in both cases.

(I’m using Git 1.7.4-rc2.)

Anders