A recently leaked Apple service document obtained by MacRumors confirms what many already suspected: the newly introduced silicone membranes discovered by iFixit that are beneath the keycaps on the new MacBook Pro keyboard aren’t just there to muffle sound. They’re also there as a protective layer to block dust and debris from interfering with the sensitive butterfly mechanism that has proved so problematic for some users.

When Apple announced its latest MacBook Pro updates last week, one of the more notable changes to the hardware was a third-generation version of the much-maligned butterfly keyboard. But Apple insisted that the only real difference was that the updated models were quieter.

Thanks to iFixit, we know that the reduced noise from the keyboards is due to the addition of a rubber membrane under each key. The repair document is the first direct confirmation we’ve had from Apple that the membrane is specifically designed to protect the new keyboard from encountering the same problems as its predecessors.

Per the document:

Keyboard and Keycaps 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.

Apple recently acknowledged that some users of the 2016 and 2017 MacBook and MacBook Pro laptops with earlier versions of the butterfly switches were experiencing issues with their keyboards, and it offered a four-year extended warranty problem to deal with any issues. Interestingly, the new 2018 models aren’t included in the warranty offer, and Apple won’t be using third-generation keyboard parts to repair problems on older models. That’s a shame since the ever-increasing evidence seems to point to the fact that Apple has managed to solve the keyboard problems in a more substantial way on the newer models.

The only question that remains is: why won’t Apple just acknowledge that there was a problem that it fixed? The company is potentially facing class action lawsuits over the keyboard troubles, so that might at least partially explain the silence.