The properties/actions/logic in the ItemViewModel have nothing to do with the entity's persistence state. They are purely for the current UI. It's a separate concern that has no business in the entity. If you later on decide to change the UI the need for the current ItemViewModel may go away or requires enhancements. Neither one should require a change to the entity.
This is also captured by the Open Close Principle (OCP). Changing the UI should not result in a modification to the entity.
http://c2.com/cgi/wiki?OpenClosedPrinciple