Hi, this is fixed in 7.3: https://docs.mendix.com/releasenotes/desktop-modeler/7.3#730
"We fixed the server-client serialization of changes for read-only date, Boolean, integer, long, and reference set members. (Ticket 52317)"
Ran into this issue also. Even the default mendix projects from the appstore have this issue.
I think it has to do with committing and entity acces. A quick work around is using a different entity to display the date. And then pass that date to the "real" object in the background.