Got a similar problem with an APC Smartups 450RM serial UPS.
As a temporary workaround I added commands in apccontrol to issue the killpower before starting the shutdown. I've had to up the shutdown delay to 3 minutes and up the lowbatt and lowruntime levels to ensure I can shutdown cleanly, but so far, it looks ok.
I'm no expert, so I expect I've missed something...
Got a similar problem with an APC Smartups 450RM serial UPS.
As a temporary workaround I added commands in apccontrol to issue the killpower before starting the shutdown. I've had to up the shutdown delay to 3 minutes and up the lowbatt and lowruntime levels to ensure I can shutdown cleanly, but so far, it looks ok.
I'm no expert, so I expect I've missed something...