Validate in Mock Message Viewer

When I validate (Alt-v) an invalid request message in the MockService message viewer the validation returns with an info box "Validation OK" (even thought the message is not valid).

When I copy the same message to a new Request for the same operation and validate it there the validation error is shown correctly.

Is the validation in the MockService message viewer broken?

Used Version: Soap-UI 4.0.0 (but also happens in 3.0.1).