Thanks guys. Pretty soon, I'm going to have to pin the majority of my packages to the dev release. Not that it's difficult to do thanks to the awesomeness of opam, but I feel like this doesn't necessarily make for an environment that's kind to beginners, who wouldn't be aware of these things and just bump into issues, eventually giving up.
IMO a bugfix for an issue in a released version necessitates an opam release. This issue is much worse, because it relates to .merlin files created by jbuilder.