Like Andrew wrote your idea is wery interesting in case of motor issues. I tried to find some answers. I reviewed carefully the Bluetooth documentation and didn't found any information about mentioned flag. It can be found at other document but I do not see any relationship between this flag and the direct communication protocol. Can you please share with me the source code of the program you described here?
Then I wrote a C# program (using Visual Studio 2008) to open a BlueTooth connection to the brick and sent integer values to mailbox 1 at the NXT brick.
You was using MESSAGWWRITE? I would like to review your approach and try find some answers.