Muse 1.0.1, as it comes with Fedora 13 i386.
When you first add a fluidsynth (not fluidsynth-dssi) to Muse, the gain comes up at a very low value, like the third mark from the lowest setting. This is really attenuated.
If you change the soft synth's gain setting to a reasonable level, on the soft synth's gui dialog, then save the Muse project, exit Muse, then restart Muse and reload the project, the soft synth's gain is back at that low level instead of where it's supposed to be.
I've been using Muse for a long time under Fedora 9, and this problem just showed up when I upgraded to Fedora 13 (newer Muse, I presume).