While these claims (the dangerous part is already a given) will still require years of observation and research, the fact is, polar bears are simply built to prey on other animals. Sometimes, it may very well be their own kind. Instinctively, they claim high marks for their hunting abilities.
Let's look at what they do to capture prey. Fist, they have a keen nose for food, especially seals. Experts believe they can sniff those tasty morsels up to 20 miles away. Polar bears have been known to sit for hours near a hole in the ice, just waiting for a seal to come up for air. On land, when they're on the prowl, polar bears really get sneaky. Moving slowly, crouching low to the ground, they blend in with their snowy background. One drawback: their black noses. So, what do they do? They've been known to use a huge paw to cover up.
Their bodies are a surprising heat sources, keeping them warm while living in the coldest parts of the world. Their skin is black, hidden underneath light-reflecting hollow hairs. When the sun shines, it absorbs the warmth. Compounded by a layer of fat, they're well-insulated and ready for the hunt.
As far as the nuisance aspect - they're also natural wanderers. Again, when food is scarce, they'll travel for hundreds of miles in search of food. Sometimes, it means pilfering trash cans.
My point is that this is likely nothing new. Polar bears are just doing what comes naturally.
Polar bear walking alone. Credit: USFWS