Comment 3 for bug 1222132

I pushed a fix for the case of repeated validation here:

https://github.com/lxml/lxml/commit/4c748a9f8bb97a20f0f6948f3a426f02137f6d6d

The same applied to RelaxNG and Schematron. DTDs were ok. It'll go into lxml 3.3.x.

Note that this change does not fix the multithreading case, which would be a backwards incompatible change. I'm therefore leaving the ticket open for later reconsideration.