RANCHO CORDOVA (CBS13) – If you come across a bear, that bear’s first instinct should be to run away, but researchers with the California Department of Fish and Wildlife have come across some bears with very odd behavior.

“Someone opened the trunk and it climbed in the trunk and that is not normal behavior. And that’s got to be a red flag right? That’s got to be a red flag that something is not right,” said Dr. Brandon Munk.

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The California Department of Fish and Wildlife Senior Wildlife Veterinarian started studying these overly friendly bears in 2014 at the investigations lab in Rancho Cordova.

Researchers at UC Davis even performed CT scans to determine what was causing the peculiar behavior. Necropsies showed the bears had encephalitis, a neurological disease that causes inflammation of the brain, but there’s no telling how they’re getting it.

It’s shown up in four bears over the past year. They’ve been found in several counties including El Dorado and Tulare.

“We started seeing something strange, I believe it was about five years ago,” said Ann Bryant, executive director of the BEAR League, a non-profit based in the Lake Tahoe basin.

Bryant remembers one of the bears walking right into a school full of kids and making himself at home in the classroom.

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“He sat in the back just like a puppy dog. That was not normal. That bear should have been terrified to go into a building with a lot of people,” said Bryant.

What’s complicating things for researchers is that the bears appear normal, but just friendly. Some even appear healthy with good-looking fur.

“Right now there are just so many unknowns about this but yet it’s out there, it’s happening,” said Bryant.

It’s a wildlife mystery but researchers are reminding everyone that friendly doesn’t mean safe.

“Next thing you know, maybe I’ll just hand feed it and see if it takes it out of my hand. You know those are situations where you’re getting a lot closer to getting bit potentially,” said Dr. Munk.

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Experts recommend you call wildlife officials or the BEAR League if you spot a bear behaving oddly. But they urge people not to approach them.