It's strange, I know, that while I like case sensitive filenames, I don't actually want to be bothered matching the case exactly when I'm using tab completion. Fortunately, emacs and bash both accommodate my whims. For bash, add

set completion-ignore-case on

to your ~/.inputrc file. For emacs, add

(read-file-name-completion-ignore-case t)

to your emacs initialization files. Of course, if want to get rid of all completion case sensitivity, you need

(setq completion-ignore-case t)

too.

Thanks to the wonders of Google and Ruben I finally found the answer: remove (you'll want to make a backup copy before you remove it, though) /etc/setup/bash.lst.gz which apparently had become corrupted.

According to a comment on that post, running gunzip -t on all files in /etc/setup will tell you which setup files have been corrupted.