Screen won't lock when idle using battery

[Luciano S Cassemiro]

Hi.
I noticed my Kubuntu 14.04 won't auto lock screen when using battery.
It does work when plugged.

Am I missing something or is this a known bug? Could not find anything 
online.

Current settings (battery): Dim display after 4 min. (works OK)
Switch off after 8 min. (works OK)
Suspend session after 10 min -> Lock Screen.
-- 
Luciano S Cassemiro
lcnx at moto24h.com.br
http://www.moto24h.com.br