Aha, here comes the problem with inheriting controls and using the designer. If you set a property in a base class, the designer adds it to the code of the InitializeComponent() method, which gets called by the inherited controls as well. Then, if you set the property back to its default, the subclass designer thinks that it doesn't need to generate code for it, so it does not serialize it (bold it). But, since no code was generated to set it back to the default, the base class's code to set the property takes over. Kind of a pain if you ask me. The problem is being able to control the ShouldSerializePropertyName and ResetPropertyName methods, which are defined in the class that defines the property. Since the property was defined in the base class, it controls whether the value should be serialized.
Long story short, the only way to fix it is to set the proper value within the subclass, programmatically. If component designers were smart, they would make the ShouldSerializeX and ResetX methods overridable, but I've never seen a control where they were.