I this exact problem with my droid1, where even tho I had the phone locked with the pattern, my bluetooth headset somehow was able to trigger a call to the last person that the phone called. I never found a fix for it on that, and I just assumed this would be fixed on the droid 3.
I also saw there is a option "Allow Bluetooth Bypass" under security that comes off by default, and I have checked to make sure, and it is still turned off.
Now it just happened to me on my droid 3. I was actually looking at the black screen on my droid3 (it was locked and off), and then a button must have gotten pressed on my bluetooth, and then it called the last person dialed.
I have the Plantronics 925 Headset Right now:
Amazon.com: Plantronics Discovery 975 Bluetooth Headset: Cell Phones & Accessories
Do it seem like the headset is defective?
But either way, the droid should not be making calls while locked, I don't understand while this keeps happening even in the 3rd generation of the droid.
Anyone have any ideas on this or see this also happening on the droid3?