Oddly enough, i have yet to see it happen with direct flex. I've spent a bit of time today launching apps that have a directflex configuration, however it never ceases to launch almost immediately.
This isn't too big of an environment, our VDI may hit 125 concurrent users. The latency and network utilization for the san is low for all datastores. The compellent is connected via 4X10GB fiber ports to a 2 Force10 switches in the back of our m1000e chassis.
We use McAfee move for our VDI and have setup all of the exceptions, I've actually read the article you've referenced. While i was fixing this environment i was crawling this forum and googlefuing a bit 
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I'm going to get some time stamps and start looking through the logs on the hosts themselves and see if i can glean anything from it. The behavior is odd to say the least, and there has to be something somewhere that can point me in the right direction.
Appreciate your feedback though.