The only relevant experience I can give you is that DD was giving us the business after 2 months of tear-free preschool drop-offs. I asked the teachers what happened after I left, and they assured me that after about 30 seconds she was OK. So one morning, I decided to stick around and see for myself, and they were right. She whined and fussed when I was leaving, then I ducked around a corner and peeked through the secondary class door where there was a tiny gap in the blind, and sure enough within a minute she was fine and playing with friends. Sooo, I find it conceivable that your kiddo could be OK playing with others, and then when she sees you she remembers, 'hey, I missed her!' and go into whine mode.
PLUS, it is a very well known fact that most kids save up their worst behavior for those they feel closest and safest with, becasue they aren't afraid that person will stop loving them. I repeat that sentiment to myself a LOT some days.
