Dates not found in current path (v0.7-alpha)

I am encountering this:

ERROR: LoadError: ArgumentError: Module Dates not found in current path.
Run `Pkg.add("Dates")` to install the Dates package.

while working on some local packages and scripts, but not others. (Dates is in stdlib, so this is just wrong.) I vaguely recall mention of peculiar problems with Dates, but have been unable to find it again with handy search facilities. Can anyone point to an official issue and/or workaround?

Possibly related: Sockets module not found (v0.7)