Comment 1 for bug 754038

These happen when the WADL is served, which sometimes (for unknown reasons) seems to decide that it needs to actually generate WADL rather than serving the pre-rendered file. Generating the WADL looks like it uses a global (_PYDOC_PARSER) which would explain this as simply some non-thread-safe code.

Switching to Apache, as we are doing for bug 607961, should solve this problem as well.