[Evolution] free entry field in search

["@web.de" <pfeifer_s web de>]

3.28.5-0ubuntu0.18.04.2

What's behind search in a free entry field?

I was searching for 'regine' in the search bar with free entry field
activated and got a results list, but some expected entries are
missing. If I change the search term to '@', the expected message with
'regine@' inside the from field is part of the results list.