conda-forge.github.io: Installing from conda-forge breaks conda's installation

I tried to install cookiecutter and jupyter_contrib_nbextensions from conda-forge. In both cases, the last step in the plan was:

The following packages will be DOWNGRADED:

    conda:           4.5.0-py36_0                      --> 4.3.34-py36_0    conda-forge

Going forward with this ends up with a broken conda installation!!!

I opened an issue on https://github.com/ipython-contrib/jupyter_contrib_nbextensions/issues/1267 but I believe this is a more general problem given that it happens also with cookiecutter.