Can't search on custom column, multiple criteria

[bob.f]

Hi,

I have a custom yes/no column in calibre, accessible in CC, denoting whether I have read a particular book.

If I select Groups / Read, long press on <<>> and select Matching, I get "search "read:"="" matched x books. All good, and all my unread books are displayed.

If then tap the search bar, I see the same criteria highlighted. If I then hit search again (with Faster search off) making no other changes, I get "search read:"="" matched no books.

What I'm actually trying to achieve is a combined search like #read:"=false" and author:"=xxx".

I can do this by long pressing a group to filter, then then short pressing another group but I'm wondering if I can do this using pure text search syntax, as I may want to use more than two criteria.