The search query syntax uses OR as the default conjunction operator: "The OR operator is the default conjunction operator. This means that if there is no Boolean operator between two terms, the OR operator is used."

This appears to be copied verbatim from the Lucene documentation: http://lucene.apache.org/java/2_3_2/queryparsersyntax.html and I'm assuming it's the Lucene default behaviour that's showing through in Jira.

We don't consider this to be a particularly useful default and would much prefer AND to be the default conjunction. It seems very easy to ask Lucene to perform searches this way, so I was wondering whether Jira could be configurable to call Lucene that way?