Battery Fully Charged turns off AC

This problem started 3 weeks ago.

When battery charge reaches 100% the AC LED indicator is turned off and the laptop runs from battery (decreasing it's performance even selecting High Performance power plan).
If the AC plug is disconnected and reconnected the AC LED indicator is turned on until battery is fully charged again, as soon as the battery is fully charged windows battery notification icon changes from "99% available (plugged in, charging)" to "Fully Charged" and then the AC is turned off and the laptop starts to run from battery again.

I didn't update any laptop specific software nor BIOS.

Last installed windows updates:
Caption Description ID InstalledOn
http://support.microsoft.com/?kbid=2982378 Security Update KB2982378 9/16/2014
http://support.microsoft.com/?kbid=2977629 Security Update KB2977629 9/16/2014
http://support.microsoft.com/?kbid=2973112 Security Update KB2973112 9/16/2014
http://support.microsoft.com/?kbid=2972211 Security Update KB2972211 9/16/2014
http://support.microsoft.com/?kbid=2894844 Security Update KB2894844 9/16/2014
http://support.microsoft.com/?kbid=2993651 Update KB2993651 8/29/2014

Does anyone know how to fix this? I want the laptop to run from AC when AC is plugged in, even if the battery is fully charged.

Thanks!

That is not ideal because I need to use the laptop on battery very often. Besides that was not happening before.