Posting this from my six month old Macbook Pro 15" on which the spacebar has just started doing double spaces. Going to try and clean it with compressed air, but even if that works, it's unacceptable in my opinion that such a key piece of hardware on such an expensive machine should be so fragile. The fact that at some point I'll have to take it back to Apple and probably be without it for several days due to the com…
I’m experiencing this issue with my B key and it’s annoying af. I use my MBP in clamshell mode with an external keyboard and I dread going mobile.
Mine was out of warranty, so I fixed it myself.
Failed: compressed air Failed: cleaning under the key.
Success (but not recommended) I removed the key, then pulled off the glued membrane. Cleaned all with 90% alcohol. Took a new membrane (but you might be able to use old) and used E6000 and a toothpick to glue it back. Replaced butterfly and key.
Not a good solution, but it worked.
It looked like the contacts were getting coated and not making good contact? Perhaps heat?
Best of luck.