I posted bug report: 63406.
REALGetPropValueBoolean((REALobject)instance, “Enabled”, &enabled) does not work in IDE design mode
So control has no idea if it should render enabled or disabled while in IDE design mode.
This one here does work but is deprecated:
RBBoolean enabled = REALGetControlEnabled(instance);
Easiest solution would probably be to remove deprecated on the REALGetControlEnabled.