Our vendor's system has a bug affecting some of the library facet options in WorldCat UMD where materials held by a branch library are not returned when a user applies that facet. Currently, the Architecture Library and the Maryland Room Collections facets are the only 2 known to be affect by this bug.
All of the libraries' holdings are still discoverable using the higher-level facets, so if you encounter this problem, you can select a facet like University of Maryland, College Park or Libraries Worldwide.