The Application Manager for some reason does not show correctly the installation drive if it is changed e.g. by re-installing the app. You can detect the correct installation drive from Settings->Themes->Screen saver menu. There is a small icon behind the "Sleeping Screen" text. See the screen shots ...
Installed on "Mass memory"
Installed on "Memory card"
If there is no symbol it is installed on "Phone memory" i.e. C:
Hope this helps!