Apologies, I should have included further information.
This is in Chrome on a Windows Desktop, using either the Search dropdown in the centre of the top horizontal blue menu bar (click the search dropdown, type the sample search phrases from my original post, hit enter) or the search-within-this-forum option while viewing any forum.
It is matching things that shouldn't match such a specific search phrase as +"boarding bag", e.g. it finds this thread: The way how Finnair implement the new cabin bag control
.. which as far as I can tell never contains the exact phrase "boarding bag".