[git-p4] Cannot submit to perforce

With today's git:

I'm trying to reproduce the git commands git-p4 execute.

$ git branch -r
  p4/HEAD
  p4/master

$ git diff-tree -r
"0a41bb5b8387517ca5c45c56544e978b2f82f021^".."0a41bb5b8387517ca5c45c56544e978b2f82f021"
:000000 100755 0000000000000000000000000000000000000000
67406438a99bb212502eb3f3581527f046a96964 A
r3d/Viewer/qtgui/tools/buildrss.py
...
...
...

$ git format-patch -k --stdout
"0a41bb5b8387517ca5c45c56544e978b2f82f021^".."0a41bb5b8387517ca5c45c56544e978b2f82f021"
| git apply --check -
<stdin>:225: trailing whitespace.
#
<stdin>:233: trailing whitespace.
#
<stdin>:273: trailing whitespace.

<stdin>:275: trailing whitespace.

<stdin>:295: trailing whitespace.

error: r3d/Viewer/qtgui/tools/buildrss.py: already exists in working directory
...
...
...

For me the "already exists in working directory" means we are not in
the right branch, and that we are trying to apply the same commit on
the master branch ?

If I issue git-p4 submit I have basically the same output, I say
"[s]kip this patch" and it ends with:
"""
Some files in your working directory are modified and different than
what is in your index. You can use git update-index <filename> to
bring the index up-to-date or stash away all your changes with git
stash.
"""
If I retry git-p4 submit with doing the stash, sometimes the perforce
submit goes fine, sometimes not... ???

Thanks for any help,
Benjamin.