git-fast-import bug?

git-fast-import is not writing a commit even after a checkpoint/progress command.

See my previous message "git p4 diff-tree ambiguous argument error". 

The error in git-p4 is caused by git not writing the commit even after git-fast-import has been given a checkpoint and progress command.

On initial use of git p4 to sync a p4 repository, the commits are written properly. But on a subsequent run the commit is not flushed to the file system during the run. Specifically, I can stop the git-p4 command directly after the progress checkpoint command (see the checkpoint() function in git-p4). The file is not found. If I abort/exit the application at that point, the file appears. 

There is a pattern of behavior here that is consistent but I am unable to understand. A bare repository works fine. An already populated repository does not work until the app is quit. What would cause git-fast-import to _NOT_ flush the file?

This certainly seems like a bug. But I don't know enough of the git internals to reproduce.

Suggestions on how to test or isolate this problem?

Thanks

Reproduced consistently on two systems:

$ git --version 
git version 1.8.5.2 (Apple Git-48) 
$ python --version 
Python 2.7.5 
$ uname -a 
Darwin Kernel Version 13.3.0: Tue Jun  3 21:27:35 PDT 2014; root:xnu-2422.110.17~1/RELEASE_X86_64 x86_64 

and 

$ git --version 
git version 1.7.12.4 
$ python --version 
Python 2.6.6 
OS: GNU/Linux 2.6.32-431.el6.x86_64