Enabling Harpsichord registers

I'm not sure if this is a 'feature' of the update, but I've just discovered the buttons (also accessed via the bottom three keys on the keyboard) which are supposed to enable and disable the harpsichord registers in the Ruckers model. They should toggle the L8', U8' and 4' registers on and off. However, I find that they only DISABLE the registers, and when I try to enable them, nothing happens. Has anyone else noticed this?