I found this in the context of trying to run a selected test.

In a fresh squeak
get a test runner from the world menu.

Select a package from the left hand list.
Note that while the package's list of test classes  appears the item selected is not highlighted.

Note that nothing in the list of test classes is highlighted. Usually everything is highlighted.

Select one class out of the list. At some point (first or second try) it is highlighted.

Get menu while over item and ask "selected inverted"

Note no change in highlighting.

Run selected. 

Note it seems the wrong number of tests are being run.

So something is weird.

It was weird in the previous release candidate also.

Annoying. :(

Yours in curiosity and service, --Jerome Peace