An IMDb link for a film, by default, looks like this: http://www.imdb.com/title/tt0258038/

If you click on "Full cast and crew" from that page, it'll look like this: http://www.imdb.com/title/tt0258038/fullcredits#cast

If you're logged into IMDb and you set in "Site Preferences" the option to "Display full credits", all film links will look like this: http://www.imdb.com/title/tt0258038/combined

When pasting in a link like this at the Release Group level, using the Relate to URL feature, these URLs are correctly determined to be for the edit "Has an IMDb page at". But the cruft at the end should be automatically removed.