Thanks for catching this, it should be fixed now.
About your other question on #winehackers, refcounts are useful to keep waves referenced from the instrument regions, which is necessary to avoid deleting them on Unload, if they are unloaded before the instruments (this is actually checked in the test, and the unload callback -which we don't implement- for the wave is only called after the last reference to it, from the instrument, is released).
For the instruments, it's not very useful yet as there's only a single reference, but it will be useful later, when they are returned as FluidSynth soundfont presets.