I have zone files loading on Mono now.
I had a sneaking suspicion that it had something to do with the XmlElementAttribute that I used to keep the XML tags in the zone files compatible with the encapsulated, property-based classes. I spent a few hours updating the zone converter application so I could remove the XmlElement attributes. After loading the MUD on Mono, all zone files magically loaded. “All” being the ~6 that I’m officially authorized to use so far.
Since I’m running Ubuntu 9.04, the native version of Mono is 2.01, a bit behind the current version of 2.4 (which will ship with Ubuntu 9.10). Installing Mono 2.4 on Ubuntu 9.04 is not as easy as one would hope, and I can’t say for sure that it would take care of the problem. Mono has made great advances lately, so I’d be surprised if the latest version had the same problem.