Setting bbswitch to OFF prevents fan to run on Acer 5755G

Prerequisite: installed nvidia proprietary drivers, bumblebee and bbswitch-dkms packages.

When the system boots up the fan is running in normal mode. Log in to system and the fan stops even if temps are > 60° (it should be turned on at ~50° as of bios settings); it will go up and up until it reaches very hot temperatures and starts throttling (>=85°). Just issue 'sudo tee /proc/acpi/bbswitch<<<ON' and the fan starts magically. Reverting it to OFF shuts down the fan. This is a dangerous bug. I'm not sure it's into bbswitch but it's clearly related to it.

Release Elementary OS Freya 0.3
bbswitch-dkms version: 0.7-2ubuntu1

acerhdf modules is not loaded

Packages installed: thermald, intel_pstate, tlp (starting/stopping thermald does nothing about fan rotation)
Kernel load params: acpi_osi=Linux acpi_backlight=vendor intel_pstate=enable pcie_aspm=force

BIOS version 1.21