MacBook Air keyboard not capitalizing J, M, U with Shift key

I have a MacBook Air. Today I noticed I was unable to type a capital J with the shift key. I had to use Caps Lock to get it capitalized. I tried all the other letters, and saw that it happens also with the letters M and U. I googled this, and it seems that because these letters are near each other (somewhat vertically) that it isn't that uncommon. I checked, and I do not have slow keys or mouse keys checked in the Systems settings. I cleaned the keyboard with canned air and rebooted. The problem persists. Any ideas?