CYGWIN git cannot install python packages with pip

On Windows, with Cygwin-git 02.12.2-1 the python command:

    pip install git+https://github.com/...`

fails to work with the following error:

    $ pip install git+https://github.com/ipython/traitlets/
    Collecting git+https://github.com/ipython/traitlets/
    Cloning https://github.com/ipython/traitlets/ to c:\users\username\appdata
\local\temp\pip-kjwxq_oy-build
    fatal: Invalid path '/cygdrive/d/Work/ALLINONES2/co2mpas_AIO-v1.6.0/CO2MPA
S/C:\Users\username\AppData\Local\Temp\pip-kjwxq_oy-build': No such file or di
rectory
    git clone -q https://github.com/ipython/traitlets/ C:\Users\user\AppData\L
ocal\Temp\pip-kjwxq_oy-build" failed with error code 128 in None

Git-2.8.3 had no such problem.

Any ideas?