I've tested this fairly thoroughly in PVP, not so much in PVE, but I imagine it will result in the same.

With a Magus Corrupt Rescuer, their default attack has a chance to "steal beneficial effects". When the beneficial effect stolen is a titan shield or the other shield (with five dashes, each dash is lost to an attack), it doesn't actually work on the MCR.

Attacks will completely ignore the shield and go straight to HP.

I'm unsure if other stolen shields will work, but they should be tested internally as well