I've fixed heavycoin:// URI parsing issue and tested it this time / plus updated the builds, sha256 checksums, and signatures. [It was what you found, but also the length of a string replacement for stripping out "//" needed fixing too.]
Yeah, I only traversed the code a few layers deep

Crazy how many source files that one simple operation bounces through

Confirmed fixed, though! I'd paste a sample .reg file here, but I'll leave that to the installer (forking the NSIS one, I take it?) as it's less error-prone.
though if anybody really wanted to - regedit.exe, HKCR, find 'Bitcoin', export key, edit to suit Heavycoin, double-click to import, good to go. Take special care with -datadir="etc." if you use it, or you'll get errors / two data dirs.