Search function showing unrelated results

Android Version 13
K-9 Mail Version 15.0
Latest F-Droid release

Issue:
Searching returns results that do not contain the search text.
For example, when searching for “TARDIS” in a list of a hundred emails, the results will list 5 emails with the word “TARDIS” in them plus dozens that do not.

Expected result:
Searching for a word or phrase should ONLY return results that include that word or phrase. In this example, only the 5 emails that contain the word “TARDIS” should be displayed as search results.

* This behavior is consistent and repeats with every search.
* The behavior is consistent across app restarts.
* The behavior is consistent across device reboots.
* The behavior is consistent regardless of the “Server search limit” setting.

This seems to be such a basic function; one would think such a simple behavior would be easily implemented.