[Benji Sweetpea]

Hello. I'm having a problem with them darn onion skins.
I've created an animation using imported jpg's and i need to see the previous frame so that I can line up each image one after the other.
The problem is that when I use the onion skin button to view the previous frame it hides it's little ghostly self behind the image that i'm using. That aint no good. I've tried sending the image to the back to expose the smelly onion skin but it doesnt seem to do anything. The weird thing is that when I use the onion to see the next frame it works fine!!! It's just when I want to see the previous frame that it gets all shy.
I've looked through loads of manuals and guides and no soul mentions it. Is this a software glitch or is it just me being crap. do I just need to press the big flashing button infront of my eyes?

can anybody help me??