I am having the same problem. I have 2 devices now linked to one MyDrive account as it is now possible to use one common e-mail address.
If I select a destination on one device, say the 6200, then the destination changes on the other one, a 6000. This is unhelpful unless you are running both devices in the same car side-by-side.
We have two Tomtoms for my wife and I to use independently but wish to sync My Places on both. Without this facility, it is pointless having MyDriveConnect.
I have now downloaded 16.600 to both devices and it has NOT resolved the problem. It is now 7 days since the agent responded that it would be fixed and there has been a software update.
I have three top-of-the-line TomToms when they were purchased (6200 / 600 / 940) and this fault renders the 6200 / 6000 simultaneously unusable.