[BUG] git-filter-branch and filename case changes on insensitive file systems

My repo has a change where a directory named Src was renamed to src.   
When I run "git filter-branch HEAD", my repo history is  rewritten so  
it appears that the Src directory was simply deleted.  I'm using case  
insensitive HFS+.
Fortunately, I can work around this by using -d to work off a case  
sensitive HFS+ volume - "git filter-branch -d /Volumes/CaseSensitive/ 
test HEAD" correctly changes nothing.

Anyone know why this happens?

Jon