No shit Sherlock, There was discussion about why the high loop was called for in dishwasher installations. That was the point. It's perfectly clear that you not only don't have a sink, but in fact are connecting the dishwasher drain straight downhill into a sewer pipe without a trap. I think just about everyone here will tell you:
A - That's a clear code violation
B - It's one code where the reason for it is clear and it makes perfect sense.
Sigh... Once again, traps in sewer systems are not there to prevent your sewer from backing up. They are there to prevent SEWER GASES FROM ENTERING YOUR HOUSE every day. If traps aren't needed, why the hell does every sink, washer, toilet, etc have one? You're concerned that water may be running out of the dishwasher, but not that sewer gas can be coming back in? Sounds great. Cleaned dishes sitting in a closed dishwasher, exposed to sewer gas.
If it's behaving that way, then it could very well be happening. Do you think every dishwasher uses exactly the same pump out design? No one here is gonna know how your dishwasher, which you don't even indicate the make or model is going to behave when you use it in a way MOST people never would. As others have suggested, you could go to the manfacturer's website and see if you can find an owners manual. But even that will probably not answer the question. They will show how it should be installed, but likely won't tell you what happens if you do it another way.
But instead of speculating, why don't you just put a high loop in it temporarily and see if it then works correctly? And regardless, get a trap and do it right.