Usb Drive Thrashing

I decided to install Bitdefender 2012 on a new machine a few weeks ago. This machine runs Win 7 Pro (fully up to date) with I7-2600k / 8 GB DRAM, Patriot SSD C: drive and no other anti-virus on the system. Bitdefender has proved easy to use and appears to be doing a great job - no problems at all and am very satisifed except for this:

The system has 2 external USB hard disk drives. These drives thrash furiously and I have confirmed the cause is the BD vsserv.exe engine. I thought this might just be a normal scan but realized after 10 hours it was not ever coming to an end. The thrashing begins every time the machine is booted and does not cease until shut-down. CPU usage fluctuates between 5% and 10% with nothing else running. There are two workarounds discovered by trial and error.

(1) Before booting ensure the USB drives are turned OFF or disconnected. After boot, connect them and ... no thrashing. Behaviour is normal. The drives are idle when not being used by an application. Great.

(2) If your forget to do (1) there is thrashing, of course so ... open the BD Settings and turn OFF "Scan boot sectors". Thrashing ceases immediately but you must keep this option off or thrashing resumes. I don't know if turning off boot sector scan is safe and is one of the questions I am asking. You'd think boot sectors would need to be checked only once during life of a session, not continuously (???)

In Settings I have tried excluding USB drives and also Adding the drive letters and main directory paths to the exclusion list. None of this makes any difference.

Is it normal for boot sector scanning to cause continuous thrashing of external USB drives? Is turning this off safe? Why does delaying connection of USB drives until after boot prevent thrashing? Should I be doing something else? I have no real problem with workarounds but feel they should be unnecessary.

Best wishes,

JH