Hi Martin!

The intersphinx stuff is simply linking from a Sphinx RST documentation to a different Sphinx RST documentation, using support from the intersphinx extension of Sphinx. I think the name comes from the interwiki links in MediaWiki. It only comes into play here because my particular documentation is outside of the Python documentation. The same issues would arise when linking from other places in the Python documentation.

Your explanation about :noindex: hits the nail on the head, I think. It seems to me that a minimal variant for fixing this would be:

* add :noindex: to the class markup for the short descriptions of tzinfo and timezone.
* add a class markup for tzinfo at its long description.

I don't know whether that solves the method linking issue, though, but its worth a try.