iMac Keyboard Shift key glitch: more keys; more keyboards involved

Last time, we noted a Shift key glitch in Apple's USB keyboard, whereby you could get a lower case letter even when holding down the Shift key. Readers were quick to follow up with further details:

"It also happens on a MacAlly iKey USB keyboard. Maybe it's a bug in the way Apple handles USB keyboards. "(Michael Sneider)

"I've had a MacProPlus keyboard from KeyTronic for the past five or six years, and it's always had this problem. (Daniel Griscom)

The same glitch exists for the Command key as well. (Evangelos Christodoulou)

By holding down both Shift keys on the iMac keyboard, some letters won't type at all - especially the keys in the top row of letters (e.g., QWERTY). (Khalid Shakir)