Aperture's Fast Library Switching Bug and RawHide
There is a bug in Aperture related to switching libraries, which affects the APIs used by RawHide. If you use Aperture's fast library switching (i.e. The menu item File->Switch to Library) and then load the library in RawHide there is potential that wrong images could converted.
The bug is data retrieved using Aperture APIs become stale and/or corrupted after the fast library switch. The only safe way to do switch libraries is to shut down Aperture and restart it with the new library.
You should not worry though, it only applies to the communication APIs.