Sorry to bring this issue back from the grave - but I still have the problem, and I have a new clue to offer. My co-workers have had problems when connecting to PC (running Spark) when using remote desktop. In their case, they are seeing everyone disappear from their group list, and I suspect that this is more of an AD problem which has it's own open bug assigned to it. But I am not ruling out the remote desktop as being part of the problem.
It occurred to me that I use remote desktop throughout the day to connect back to my desk, and after hours from home using a VPN.
Can someone try to reproduce this using a PC running Spark and remote desktop to get into it?