Hello yt developers,
I don't know if this is a "bug," exactly, but I noticed an issue when doing a clean install of yt today involving the h5py install. Namely, it looks like if you have an non-empty CFLAGS environment variable (which can happen without your knowledge if you load certain module files in a supercomputing environment, for example), the h5py build will proceed without getting the "-fno-strict-aliasing" flag and the resulting module will not work. You can get around this either by 1) clobbering CFLAGS, or 2) adding "-fno-strict-aliasing" to it and re-running the script.
It seems like the install script should either detect this and work around it, or else warn you that the h5py build has gone of the rails after the installation, because the tracebacks you get from trying to use the whacked-out h5py module are not very illuminating. I would do this myself, but I'm not sure my shell scripting skills are up to the task.