This property (similar to "Numeric") is not operational. All what IsRequired does right now is put a checkmark into the field to make it appear as required. However the Personas client does not enforce this, just like a field that's marked "Numeric" will allow any input, not just numbers.
I already logged this as a bug internally at SAP, hopefully this will be addressed in the (not too distant) future.
Just about the only thing you can do is check required fields via a script - which is certainly a pain to do. It is not even always possible, for instance when pressing ENTER takes the user to the subsequent screen. Then the script won't be processed.
I'm certainly aware that you could link the script button to a field thus press it upon hitting ENTER but if the cursor isn't focused on an input field or some other button is pressed, then the link is ignored, so this wouldn't work.