The problem with the Sourceforge releases is resolved: all files across all releases must have unique names (there was already a file named 'multiburn' in a previous release). I must have known this when I released version 1.41, but by the time I got to releasing version 1.42 (which had turned into 1.43 by the time I got this problem resolved), I had forgotten, and I still can't see any mention of this requirement anywhere on the Sourceforge site. It looks like each project is assigned a single directory on a server somewhere, and new releases don't get subdirectoried.
Apparently, I'm not the only person that finds this annoying.