I'm pretty sure I was getting the loss of sync even prior to the source update, but as of lately it is getting worse, Population increase is probably to blame.
I was getting loss of sync issues before the source update too - mind you, I'm about as far from the server as you can get and lag has always been an issue for me. When I first started playing on the server my ping was pretty consistant around the 180 mark. For the last 3 months it's never below 350.
The lag also seems to be affecting Raid formations for me. I'm often joining raids and finding that while the raid leader can see me in the raid - none of my toons can talk in raid and don't appear to be getting the kill flags in T5. This can be for individual toons, clusters of toons, and/or my entire crew (of 18 or so). I've found the only solution in most instances is to use the raid window to quit out and reform - and in some cases a complete log out to reset all th characters.
Strix