Open Collector Comparator for Voltage Glitch Detection
Well you could easily have fried the part when applying 3V3 with no power on the comparator. This is because input protection diodes would route the 3V3 onto the unpowered 5V bus and likely exceed the diode ratings and cause possibly catastrophic device failure.

It's probably a good idea to put 100kohm in series with the +Vin pin.