Seedlings not getting rid of seed coats (and asparagus update)

Hi, all. I've been trying to grow pink fairy duster (Calliandra eriophylla, a shrub of the legume family) from seeds. So far, so good, but the seedlings often can't get rid of the seed coats. Just today I used a sewing needle to take the seed coat off one seedling that must have sprouted three weeks ago. The seed leaves were still fat and pale green inside. Another seedling of the same age has the seed leaves looking like leaves and a nicely developed true leaf. I'm hoping this one will develop too.
I also just took the seed coats off a couple of Convulvulus tricolor seedlings, though they had split the seed coats and were probably going to manage it themselves.
Is this a known problem? Am I doing something wrong, like planting too deep or growing the seedlings too cool? Should I do anything about it when it happens, or just let nature take its course? (The fairy duster's germination is fast but poor and I don't want to throw out a seedling that might become a shrub someday.)
On another subject, I posted earlier about transplanting asparagus that had already broken dormancy. I know everyone has been waiting breathlessly for the results. Well, they're all alive, but way smaller than the one I transplanted during winter. Still, I'll bet this is better than waiting till fall would have been. So you /can/ transplant asparagus that has sent up spears--but I wish I hadn't waited so long.
-- Jerry Friedman