No idea. I never tip it filter side down to clean under the deck and I've never had an issue before with it stalling out when running across a hill filter side down.
Anyone who says that "you CAN'T run it across a hill that way" has never cut a lawn in western Pennsylvania. You don't have much choice in the matter. Every lawn has a hill/slope somewhere on the property.
Also, oil didn't "run" out the filter the rest of the day. It looks like the bottom is wet, but no more pools of oil on the deck. (literally - I should post the pics)
I also had very few hills to deal with on the rest of the lawns - none that I couldn't cut going up and down instead of across.