We've just been through this too, it's horrid isn't it? Maybe it's just an age-thing, as someone else said, a little bit of separation anxiety? My LO has just beome incredibly clingy to me, doesn't want my H to do anything if you ask, but then really enjoys things once she gets past that initial 'no'.... going off topic slightly there!
Anyway, nursery seems to have settled for her. We had a week of taking in her favourite book one day, her 'baby' another day, and a Peppa magazine with loads of stickers in another day, so she had things to show to the others. This seemed to help, so maybe as you say, it's just having something familiar or that he takes great interest in around.
Hope it passes soon.
CB x
Eve Isabella 31/05/08 - 5lb 14oz
Henry Michael 24/09/11 - 10lb 1oz