I've used my Coleman stove with both the long bottle and the fat bottle, for over 10 years, at an angle, with no problems. No where in the literature does it say you can't. I have a propane torch that must be used upside down occasionally, to solder a copper line. No problem there either.
Rick,
You've been lucky.
I solder with the tank upside down sometimes too, often with no bad results, but sometimes a flare-up will occur.
LP is liquid propane.
The flame you see in your torch is the gas from the liquid propane.
From liquid to gas it expands 270 times, which allows a pretty small volume of liquid to last a long time.
The danger is that liquid may exit the bottle instead of gas.
The gas when burning in your torch shoots out a couple inches, but if liquid comes out instead, if you're lucky and it just spits a drop or two, you have a flare up.
If it shoots a stream, you have a flame thrower which expands outward in all directions, including toward you.
The reason for using/storing a propane tank upright is to allow the pressure relief valve to "be in" the gas area of the tank, so if it needs to vent excess pressure, it vents gas, not liquid propane.
A horizontal propane tank, designed to be stored/used in a horizontal position is designed so that the relief valve "is in" the gas area of the tank.
The little camp stoves that use a disposable bottle at a 45 or so degree angle use the theory that since the bottle is never completely filled, even when used at an angle (up to a point...) the relief valve is always "in" the gas portion of the container.
Can you use a disposable or other propane tank upside down?
Yes, you can, but it isn't very safe.
Rob
Waiting for "someday" will leave you on your deathbed wondering why you didn't just rearrange your priorities and enjoy the time you had, instead of waiting for a "better" time to come along...