Hello,
i enabled the module and it was working as aspected for the root user.

Other users granted an administration role and the rights to administer taxonomy theme never saw the fieldset "theme" within the taxonomy term administration.

In line 19 of the taxonomy_theme.module the user_access-function is called. There is a typo in the parameter. Correct is "administer taxonomy theme" not "administer taxonomy_theme"

Hopefully this bug reports helps someone and a fix can be applied to the file.

Regards
.nowrap