"Look up word stems" (this should be a TB-baeed, not a general setting) is off.
CT offers plenty of powerful settings for the TB, but CT users are forced to do try and error, as it lacks documentation.
I must confess I did not pay attention to this setting. In the next days I will see if this helps.
But the lack of documentation persists (anybody saying "wiki")?
It's the exact things that cause troubles.
Maybe, but I am German. Germans always need exact things, even if it results in a pain in the ass.
The Glossary option called "Prefix matching" (see it the Edit > Preferences > Glossary tab) must be involved here. It was on by default when it was first introduced but as it may cause too much fuzziness, it was off by default in the subsequent updates.
There ain't no such thing as too much fuzziness. You cannot have enough of it in life. It's the exact things that cause troubles.