Never had the problem but I am thinking of few things;
One; they are new plants and might not have established themselves yet.
The other thing is we have very mild winters this last two years and they like a bit of frost partricularly if you are forcing them!
That a point have you forced them? i.e covered them with a bucket or similar?
I think next year I would lift them out of the bed and leave them on top of the bed to get frosted a bit, then re-plant them, this might settle them down!