I THINK I KNOW!
Lemme cover my A$$ by saying right up front that I've never installed crown molding. But, I'm intimately intimate with plaster walls and I've coped more than my fair share of miters.
Loveswood said: "My house is rather old..."
If that's the case, she has PLASTER WALLS, and that means she has EXPANDED METAL corner beads where walls meet ceilings.
(only an inside corner bead instead of an outside corner bead)
As anyone who's ever done any renovations on plaster walled buildings knows, the plasterers would have put the plaster on thicker at the corners to cover the nails and expanded metal corner bead. I've seen plaster in corners that was a full 1 1/2 inch thick (instead of 3/4 inch)!
So, maybe the root of the problem is that Loveswood's wall/ceiling corner isn't a 90 degree angle like you're more likely to get between a wall and a floor. If she's got something LARGER than a 90 degree angle between her walls and ceiling, then fitting crown molding into inside corners where walls meet is gonna be darn near next to impossible to get right.
Same for outside corners where walls meet.
Loveswood: Do this:
Check the wall/ceiling corner angle with a carpenter's square.
Also, if you have some crown molding's you've already cut, try fitting them in at a 90 degree corner, between fridge and floor, say. If your wall/ceiling angle is funky, but your crown molding fits well when the corners are all close to 90 degree angles, then that's what the problem is... you're trying to fit crown molding that's meant for 90 degree angles into corners that can be considerably larger than 90 degrees.