If the foundation is plastic make sure they're wax coated (the more the better). If they still aren't drawing it out properly keep scraping the improperly drawn comb off and have them start again. The most I've had to do this was twice. It's usually only on one frame they seem to have an issue with as well. They seem to get the hint after this and it ends up fine once it's drawn.
Agree. I use plasticell which has a lot of wax coating but if I have time I coat them with wax anyway. I have also cut this particular plastic foundation in strips to start foundationless frames with good results.