At the point in the test folder t/tdir (or in Windows' speak t\tdir) still exists and contains three files: 1, 2, and CHECKSUMS

At that point, that folder is not present when testing on Linux.

I have no idea what that test is supposed to do exactly. An inserted rmtree _d"t/tdir"; did not cause the tests to PASS. I'll leave this to the Windows' experts.