Ideally to keep a strict separation of concerns you would want to keep the two models separate.
If you are developing an MVC (i.e. Model, View, Controller) rich-client application you would use a separate Model to bind to the GUI/form this is called the View Model which purpose is to present, capture and validate the data from a GUI. Ideally you would then copy this data into your Domain or Data Model which is the model you would persist.
It really depends on the application whether to go that extra mile or not, for 1-2 screen throw away apps that are just used to complete a simple task I don't really bother with it, but this approach really helps when developing large complex applications.