> Did you try running whitespace-tests with this change, and if so, did
> they pass?

Yes, all tests pass.

> If the tests pass, would you mind to please add a new test for this
> bug?

I've written a new test and confirmed it catches this problem. I also
tweaked the original patch to handle another instance of the same bug.

Patches for whitespace.el and whitespace-tests.el are attached.