FIXED: ZAGGmate keys not working
OK....
So I emailed ZAGG support and they got back to promptly.
Asked me to connect my iPad via USB cable to my computer and install latest updates, then reboot, "forget" the ZAGGmate Bluetooth device, reboot both devices, then reconnect the ZAGGmate keyboard.
I did this, but still the left and right shift keys did not work (as well as the UP and LEFT arrow keys). I emailed ZAGG again and they assessed it as a hardware problem, instructed me to return the keyboard for warranty replacement. (ZAGG requires my credit card number in advance to process this). My keyboard is, in fact, less than a year old so qualifies for the warranty, I suppose, but I live in Canada and bought it in the US on a business trip. So, I sent another reply and asked if they would be able to process the warranty to a Canadian address using a Canadian credit card...
While waiting for the reply (three days now)... I went out and bought a can of compressed air .
Sprayed the shift keys (with the power off) and the right shift key and up arrow key both started working again almost immediately!
The left shift key and left arrow key took awhile longer...
I shut off the power and gave a few shots of air several more times. finally, I shut off the power and turned the keyboard upside down, holding with one hand, and banged it onto the heel of my other hand.... And... That fixed the problem.
So, it seems that the ZAGG keyboard may be particularly susceptible to getting fine bits of particles under the shift keys.
Given that others on this forum have had this problem reoccur with successive keyboards obtained via warranty replacement ... I think I'll stick with my original keyboard for now and keep a can of compressed air handy.
Hope this helps others out there with the same problem.
Cheers.