For example, implementing a read-only property with a read-write property is not possible:

  class MyAction: Object, Action {

      public string name { get; set; }
      public bool enabled { get; set; }

      /* ... */
  }

gives the error:

  Type and/or accessors of overriding property `MyAction.enabled'
  do not match overridden property `GLib.Action.enabled': incompatible
  set accessor.

Weirdly, it works for the "name" property.  Am I missing something?

This commits describes how property overriding works in gobject:

  https://git.gnome.org/browse/glib/commit/?id=af24dbc12aa77aac3c82d39872878558cced7add