I'm not sure where that comes from. We've owned four in the last thirty-plus years and never ever saw what you describe.
They were all smart, loving pets! Plus, even though I love my kids, Most Shih Tzus never move off, go to college, call home for more money, or wreck cars :-)
I may have gotten the breed wrong. I was thinking of the type of dog who looks like Benji, if you recall those shaggy dog movies from the 1970s and 80s.
I used to know all the dog breeds, the way most guys would know all the top racing cars.