"pinfo dired-x" (for dired-x.info.bz2 being installed by emacs) opens the dir file instead. Patch will follow.
Created attachment 250363 [details, diff] proposed patch This one-liner should catch all common cases. It will still fail for exotic filenames like "dir" followed by punctuation, but I doubt that these occur in practice.
Thanks for the patch!. Applied in 0.6.10-r2.