The neck will only expand to the dimensions of the bullet, not more than the dimensions of the bullet. Therefore when you stop applying pressure, the bullet will stay where you left it and not fall through.
I'm not buying the "brass too soft" explanation.
While unlikely, it's possible the die is defective and maybe a universal decapping die got thrown in the box instead of a FL sizing die... That's all I've got on this...
Good luck, I hope this gets worked out for you - sux being unable to load when you want to!
