Maybe I should also add that this partner has been a nightmare to work with for well over a year, so perhaps some of my annoyance with them in general is shining through. They have certainly talked down to me before in a very transparent way, when in fact they were the ones in the wrong, so I don't feel all that bad.
For example, there was a multiple day e-mail back-and-forth debating XML namespaces for SOAP requests on another related project. My code generated XML with different namespace labels than those in their examples, so they told me it was "incorrect". I had to send them the specific section of the SOAP spec to illustrate that the labels can be anything as long as they are set to the appropriate URI -- they're labels. They didn't believe me, thought that the differing namespace labels were what were causing the requests to be rejected on their end...until a few days later when it turned out that it was a completely unrelated bug in their system.