What you've experienced happens from time to time with almost every wood burning appliance when the conditions are right.
In the last 10 years, I've had 3 different OWB's sitting on my slab- first was home built, second was an Empyre Proseries 100 Gasser, and now my P&M 250. All three have produced fireballs. It is the nature of these beasts. Before them, I had a Consolidated Dutchwest Federal Airtight catalytic stove that would attempt to knock me over from time to time. About a half dozen of my neighbors have OWB's, and every one of them experience what you're describing a dozen or so times every year.
Growing up, we had an Ashley free standing wood stove that would blow back on us from time to time. All of us in our family learned at an early age that it is entirely possible(and likely) at some point to lose eyebrows and eyelashes if you do not exercise caution (dad called it common sense!) while loading.
Just open your door wide and wait about 5 or ten seconds before you put your head near it.
Don't worry about the creosote in the firebox either. Your 250 gets the vast majority of it's thermal transfer from the horizontal and vertical tubes.
Also, try to only load enough wood to get you by until your next 'feeding". If you are down to 6' or 8" of coals, you are pretty much guaranteed to not have any blow backs. If you are still half full, you best be standing back!