Not a bug but a difficulty for users:

I do often not really understand how assignements work for CAS:

Given a variable $a$ with value, say, $\pi$, set $b:=a$ and set now $a$ to, say, $e$. What is the value of $b$?

As I understand the answer depends sometimes on the context (working with symbolic variables, vectors, floating numbers etc.) and the exact behaviour is sometimes difficult to guess for me.