I've seen this in people too. I think in many cases, it is a lack of connection with their own body. For example, I had a student who when he did bong sao, his shoulder would always come up, but when I isolated the movement, without anyone giving him pressure, he was able to do it. No sooner did he start chi-sao, or lop-sao drills, then his shoulder came up. So it wasn't a physical abnormality, but his own lack of 'connection' (proprioception?) with himself. Beginners simply do not feel what they are doing wrong with their bodies.
How many times have you said to a student, "Bend your knee." and they say, "I am!" and of course, clearly, they are not.
If I had a dollar for every...(sigh)
"My Gung-Fu may not be Your Gung-Fu.
Gwok-Si, Gwok-Faht"
"I will not be part of the generation
that killed Kung-Fu."
....step.