So initially, it worked fine. I set up HB after a hiatus, and got to the healing.
Then, after coming back one day, the two spells (Lifebloom/wild growth) bound to mouse 4 and 5 didn't work. The rest did. Binding them to alt-clicks of the more mundane mouse 1-3 works as well. Just no 4/5.
Then, I go into HB options, reset spells or just touch m4/m5 and close, and mouse 4/5 work again. Strange.
A pattern developed, and I think I've gotten it reproducible. After I quit the game in Balance spec, and reenter, and switch to Resto, mouse 4/5 stop working. Until I go into the options and reset. I coped Resto spells to all specs, and after a /reload, that worked as well.