This has happened 2 times to me now. Deimaginator catches me after I've clicked on street sign to switch streets. Due to slow connection, it takes a while to switch streets. I can see me waiting, but can't move (as I'm waiting to switch streets) and in that time, deimaginator walks up while I'm frozen and ... no more quest.
Would be nice if people with slower connections could do this quest without being caught unfairly! I can understand being caught when you touch deimaginator, but it seems unfair he can get us when we're frozen between streets.