Uninterruptible Power Supply not shutting down Mac Mini running Yosemite

We just received a brand new Mac Mini, which came with Yosemite pre-installed. Our UPS is set to shut down the computer after running on battery backup for 1 minute. I have tested this with an iMac running Mavericks (10.9.5) and the UPS behaves as expected, but on the Mac Mini running Yosemite the computer does not shut down and just continues to run off the battery.

Updated to add: I tested with the CyberPower 825VA and the Mac Mini running OS 10.10.0. Today I installed OS 10.10.1 update and tested again with the same results. I also tested with a Furman F1500-UPS in place of the CyberPower unit and there has been no change in the behavior.

Updated 11/28/2014--I have verified in Terminal that "haltafter" is on and set to 1. I also tried triggering a shutdown by "haltlevel" 100 (shutdown when battery dips below 100%) and the machine is still not shutting down. I tried booting from an external drive that has OS 10.8.5 on it, but the Mini would not let me do this.

Updated 12/01/2014--I booted the aforementioned iMac from an external Yosemite boot drive and it displays the same behavior as the Mac Mini. No progress on the issue thus far.