Presence of a search item left in the search box in one mail folder blocks the listing of emails in another folder, even though the search term does not appear in the search box when the other folder is open.

example:
Open a mail folder called oldmail2012. Search for cows in the message body of email in "Current Folder" called oldmail2012. The search box will show the word "cows" in the search box. Results of the search are displayed in that folder's mail listing. Only mail with a message body containing the word "cows" will be shown. all good.

Leave that folder as is with its search results and search box with the term "cows".

Go to folder called inbox. The search term "cows" will not appear in the search box, yet the mail listing in folder inbox will only show mail that contains the term "cows" in its message body.

Evolution search therefore seems to do two things wrong. It applies the search of the folder oldmail2012 to the folder inbox even though I specified search in current folder only. Secondly, it does not show the search term it used to select the displayed mail. The result is I see an abbreviated listing and I don't understand why the listing is abbreviated because no search term appears in the search box.