Transport buttons on my Apogee GIO not working properly

I've been using my Apogee GIO with MainStage 3.2.4 pretty happily for a while now, and once I figured out how to reliably map hardware controls to parameters, it's worked just fine. Until recently (maybe coinciding with the OS X 10.11.4 update?). I typically map the "Return" button on the GIO to mute one or more of the audio channel strips, and the "Record" button to the MainStage tuner. The buttons themselves still work just fine, but they don't light up unless I click the appropriate button in the MainStage display (and once I click the "Tuner" button in the MainStage interface, the "Record" button on the GIO stays lit indefinitely). This is a problem if I've got another window (say a plugin window) open that obscures the "Mute" or "Tuner" buttons in MainStage.

Typically the problem here would be that I forgot to send the value to GIO in Assignments & Mappings, but I've verified over and over again that this is set properly.

All the other lights on the GIO (the stomp buttons, in other words), not only light up properly, but light up with the correct colors as defined in MainStage. All of the buttons are set up identically (Port 1 GIO, Channel 1, press/release, MIDI thru, and Send Value to Port 1 GIO), so it's completely unclear to me why the "Record" and "Return" buttons no longer work (and what changed that made them stop working). This is true in all my MainStage concerts. Moreover, the transport buttons work properly, and light up properly, in both Garageband and Logic Pro X. So the problem has to be specific to MainStage.

Any ideas?