Over the years, users have reported a variety of issues with counter-intuitive behaviour of Bugzilla's Advanced Search page and particularly with the Custom Search portion of that page.  As part of the UI modernization effort, we should improve the Customer Search UI to be easier to use and to avoid the counter-intuitive cases.

One of the more common counter-intuitive cases is where users want to find bugs where one of the multi-value fields is "empty" (i.e. bugs that have no instances of that field).  To make this work the user has to formulate a search that says "Not : Alias : is not empty".  Bug 1254930 is one of several reports of this kind of issue.

Another issue is that the Custom Search criteria presents the same set of matching criteria for all fields types, even though some may not be applicable to every field type.

There are probably other issues too, and we should collect them here rather than filing each one separately so that we can address search problems in one go instead of doing it piecemeal.