Search field wiped when changing attribute

When I enter a custom search then the default search field is 'From'. When I decide, after typing a string into the search fields itself, to search for a different attribute e.g. 'Common Headers or Body' then the search field is emptied and I have to retype the string.

That also happens if one changes the delimiter (is, is not, contains, does not contain) selection.

This behaviour is only recent.
I am running Version 1.9.7 (5419) on Sierra 10.12.6

--Olaf