Works for me, keep an eye on what selection step you are on. If you try to confirm after selecting the target, you might go past the tool selection which could void the entire operation.
It works for me too! You must be select the target body and after select the tool body(remember: don't press the mb2 after selected the target body). If you are receiving the message: non-manifold solid, you have a zero thickness on this step.
"A" and "B" are solid rectangular blocks created in UG NX
"B" will become two blocks if subtracted with "A" when the keep tool is not selected
Subtract failed when "keep tool " is selected.
All other conditions same.