Odd Issue With My Cyberpower 1000PFCLCD After Power Outage

I have an older model Cyberpower 1000PFCLCD, which does not have any front USB ports, and no tilting display.  About a month ago, it was plugged in during a power outage, and when power was restored, the display stopped working.  I could get only a beep from the power button, but no other signs of life on the unit.  The power button, which is normally illuminated, was not lighting up, and none of the buttons appeared to be working either.  I tried leaving it plugged in for half a day with nothing connected (to charge the battery), but that did not help, so I swapped it out for another UPS that I had, until I could get back to check it closer.  Today, I had some time so I tested the voltage of the single 12V battery, and it was 12.8V.

​I decided to try connecting it to a PC using the Cyberpower PowerPanel Personal software to see if I could get any response from the UPS that way.  I had to dig up an old USB A/B (printer) cable to connect it, but once hooked up, the UPS was detected, and indicated that everything was OK... But even more strange, when I connected it up, the panel and buttons started working again.  I unplugged the USB cable from the PC, and toggled the display button and it was working normally after that, and the power button is also illuminated again.  So it's odd, but I thought I'd post it here in case it may help somebody with a similar issue.

While I had it connected up to the PC, I also updated the firmware and ran the self-test, which passed.