I saw that other thread and read it carefully before posting this report. While there may be something similar at work, the behavior described in these two cases is indeed different.
I think it's very likely that the two issues are different, but due to the fact that techs at FileMaker have only been able to recreate the bug in the other thread by holding down a modifier key, there may be some "cross connections" here and I wanted to point that out to TSGal and TSTuatara--whoever next responds to that thread--so that they can investigate that possibility.
Thank you for posting the descriptions and link to TechNet.
I have tried to replicate this behavior on my iMac, and am not able to do so. I have FileMaker Pro Advanced, 11.0v4 on OS x 10.7.
After enabling the LastPass extension in Firefox, I created a test database file with a field to duplicate. The field did duplicate with the option/drag.
Would you please provide any other details about your system configuration hardware and software that we can use to try and narrow this down?