rebase -i reword runs pre-commit hook with curious results

["Neal Kreitzinger" <neal@rsss.com>]

I'm confused on why and/or how interactive rebase runs the pre-commit hook 
when doing the reword command for commit (a).  My pre-commit hook does 
keyword expansion on the worktree copy of the modified index files and then 
re-adds them to effect a user-date-stamp when committed.  However, the 
user-date-stamps don't get updated when reword runs the pre-commit hook. 
IOW, the pre-commit hook does not get the same results as if I were doing a 
commandline git-commit of a modified index.  I suppose reword is protecting 
the preservation of all the contents of commit (a) except the commit message 
which makes sense, but I don't understand how it goes about doing this while 
still attempting to somehow honor the pre-commit hook.  (git 1.7.1)

v/r,
neal