ZBook 17 powers on automatically when the battery is removed and placed back

Question

Hi all,
I am an IT engineer with a 15 years hands on experience and troubleshooting skills.
2 of the laptops I own are ZBook 17.
One is a UK import (F0V53ET, manufactured in October 2013) and the other is a US import (D5D93AV, manufactured in April 2014). Both of them are running the latest BIOS revision (v01.21).
The strange problem I encountered is as follows:
At the D5D93AV when the AC and the battery are removed (i.e. for upgrading the RAM), when the battery is placed back in, the system automatically powers on. Same applies if there is NO battery attached and the AC plug is attached.
At the F0V53ET, this does not happen (and the normal is NOT to happen).
What I tried to do so far to see if the problem is resolved at the D5D93AV:
1) I upgraded the BIOS to the latest version (v01.21) at both the ZBooks.
2) Ensured that BOTH the laptops have exactly identical BIOS settings.
3) Ensured that turn on the machine while on AC is UNCHECKED.
4) Ensured that there are no power on options enabled (like the timed power on, e.t.c.)
5) Tried to disable settings like "USB charge, wake on USB" e.t.c.
6) Tried to remove the CMOS battery, press the power button with no battery or AC to fully discharge, attach the CMOS battery after a minute to ensure the CMOS was cleared and placed everything back.
7) Tried to replace the OS from Windows 8.1 Pro to Windows 7 Pro to see if it has an impact to the UEFI Bios settings (i.e. any conflict with Hybrid sleep e.t.c.).
8) Tried to enable "Power on while on AC" to see if the system behavior changes. When the battery is attached and the AC is also attached, it will power on if the "Power on while on AC" is enabled (so this works as expected).
9) The problem gets reproduced ONLY when there is either no battery and the AC is attached, or when the battery is attached without the AC (i.e. after reassembling the machine after a RAM upgrade). Then it powers on automatically.
10) I also swapped the batteries between the 2 ZBooks but the issue with the US model is not resolved either. The battery works fine.
It seems to be either a BIOS issue, or a Power Board issue (hardware fault). The UK model behaves as expected, while the US model seems to have these issues.
Any ideas will be really useful.
So far this is what I did not try yet (due to lack of time):
11) To attach the US model to a docking station and see how it behaves.
12) To disable or enable the Hybrid sleep from the Bios (instead of leaving this to AUTO).
13) To replace the CMOS battery (swap them between the 2 Zbooks), although I don't think it might be the battery as the US unit is NEW with 12 hours of use.
14) To completely remove (or swap) the Optical drives and see if the problem still persists. I know there are some really rare occassions that the Optical drive might be partially faulty and short circuiting. It may sound crazy, but I have seen and experienced this more than 3 times espexially at desktop machines.
Any info or tips will be useful, although I am afraid I may have to escalate it to the 3rd line of HP as it is a really odd issue.

Answer 1

Hello, @panoulix 
To get your issue more exposure I would suggest posting it in the commercial forums since the HP ZBook 17 Mobile Workstation is a commercial product. You can do this at Notebook - HP ProBook, ZBook, EliteBook, Compaq, Slate/Tablet PC, Armada, LTE.
The support page for your product may be helpful in the meantime:
HP ZBook 17 Mobile Workstation.
I hope this helps!
Thank you for posting on the HP Forums.
I worked on behalf of HP.