No, the onboard regulator is probably overheating, shutting down, cooling off, powering up, heating up, shutting down, wash/later/rinse/repeat.
(12.3v - 5v = 7.3v…7.3v @ 160mA = 1.168watts of heat dumping off the regulator)
(9v - 5v = 4v…4v @ 160mA = .64watts of heat dumping off the regulator, almost 1/2 as much as the 12volt case)
For the heck of it, hook up the 12.3v source and blow on the regulator itself and see if it runs longer between resets.