Turns out the membrane in Apple’s redesigned Touch Bar MacBook Pro keyboard really is supposed to help keep debris away from the butterfly key mechanism. Apple’s public statement is the redesign is just to make the keys quieter, but an internal Apple service document MacRumors got ahold of says otherwise. From the document:
The keyboard has a membrane under the keycaps to prevent debris from entering the butterfly mechanism. The procedure for the space bar replacement has also changed from the previous model. Repair documentation and service videos will be available when keycap parts begin shipping.
Of course, Apple doesn’t want to publicly admit there’s a problem with the keyboards on previous MacBook models because of the growing number of lawsuits claiming they’re defective. Odds are there are a lot of attorneys really happy this document leaked.