I've been trying to resolve that for a week.
It has something to do with a combination of ACPI and PowerDevil. There are some settings that PowerDevil doesn't immediately pick up on. When you plug in your laptop ACPI (and to a lesser extent acpid) may pick up the adapter setting, but PowerDevil will not change. For example, if you check /sys/class/power_supply/BAT0/status it may say "Charging", while if you look at /sys/class/power_supply/ADP0/online it will give the number 0, indicating that it's not plugged in. Something is not getting reported correctly.
When I start up my laptop without it plugged in pclos will sometimes behave properly. Also I messed around with the modules that are loaded. I tried starting and stopping ACPI and acpid, but those don't seem to help.