Dogs like to shred things. Some dogs like it more than others. No, I wouldn't say they're misbehaving (though if they are, remember it's always the owner's fault!). They're actually doing pretty well if they don't mangle your stuff. If you don't want them to chew up their expensive beds, just give them old blankets from Goodwill, or no beds at all until they grow out of the chewing stage. Dog toys are meant to be shredded.