At ETH Library, we use UDK classification. The UDK notations are always in capital letters, and some contain words as “AND” or German “UND”. “AND” and “UND” are defined as Boolean operators in our Primo VE. This leads to the following problem: when a user clicks on an UDK notation that contains such a word (e.g. on “PFLANZEN + BÄUME + BLUMEN (MOTIVE IN KUNST, LITERATUR UND FILM)” in this record: https://eth.swisscovery.slsp.ch/permalink/41SLSP_ETH/lshl64/alma990015558430205503), a search for “subject equals exact phrase” in the advanced search is triggered. Although a phrase search is performed, the word UND is interpreted as a Boolean operator, and therefore the search returns 0 results.
We think that the search in Primo VE should be improved so that no word in a phrase search is interpreted as Boolean operator. Since it is not possible for a phrase to contain a Boolean operator, the current search behavior is a bug and should be fixed.