Reproducible, corrupt packfile after fresh

I'm a heavy user of git-svn and experience an issue with one specific (git-svn) repository: 'git fsck' reports a corrupt packfile after every checkout.

Now I'm totally puzzled about the cause and what do about it. This is what I do:

    git svn init -s http://svn.foo.com/myproject myproject.git
    cd myproject.git
    git svn fetch         # Much more reliable than 'git-svn clone'

This checks out ~2100 commits and executes 2 git-gc during checkout. The final .git repo size is about 940MB. Then I run

    git fsck

➜ myproject.git git:(master) git fsck
Checking object directories: 100% (256/256), done.
error: packed 0f5f33639bfc1a781fe080c31a1f076d9a25c1d3 from
.git/objects/pack/pack-6a6f5355584a5d71215d5fc867ce09602ceab533.pack is
corrupt
*** glibc detected *** git: free(): invalid pointer: 0x00007f46a09e9010 ***
======= Backtrace: =========
/lib/x86_64-linux-gnu/libc.so.6(+0x7eb96)[0x7f46d9ebab96]
git[0x4ddf46]
git[0x4b4123]
git[0x431524]
git[0x405ce8]
git[0x4050e2]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xed)[0x7f46d9e5d76d]
git[0x405529]
======= Memory map: ========
00400000-0055f000 r-xp 00000000 fc:01 12452043
 /usr/bin/git
0075e000-0075f000 r--p 0015e000 fc:01 12452043
 /usr/bin/git

....

This only affects this very particular git-svn repo (and I have dozens of them). The error happens reproducible on every fresh checkout as described above. The backtrace does not appear always. The object is a very large blob

    git show 0f5f33639bfc1a781fe080c31a1f076d9a25c1d3 | wc -c
    39524691

Any hints what to do?

Thanks
- Ben