Thank you, Dan and Gerv, for your help. I read the license a bit closer, and it is a modified version of the QPL (with the "obnoxious patch clause" written out; modifications can be made directly, but that doesn't concern me as I'm using the library as-is).
So this basically comes down to the same problem of somebody wanting to write non-QPL'ed free software with Qt. If I recall, in that case, Trolltech eventually had to duel-license Qt (Free Edition) in order to let people program GPL'ed programs with KDE (without adding exception clauses to the GPL); the QPL explicitly allows any other copylefted license, but the GPL doesn't allow linking to code with the restrictions that the QPL imposes (e.g.: giving the initial developer special rights to third-party modifications, like the NPL). Is there the same problem with the MPL, or can it link to QPL'ed code with no problem? I'm not worried about a lawsuit or anything (the MPL or GPL is almost certainly in line with the spirit of what the library-writer wanted, if not the letter); I just want to do "the right thing", and learn more about the fascinating (if somewhat convoluted) world of open-source licensing. :) -Matt
