> Multiple assignment to a vector causes different names pointing to the same object.

It is not multiple assignment that causes the problem.  The problem is that the left-side argument to $ is evaluated before being duplicated, as are most operands to most operators.  So both of the following will work, producing two distinct vectors:

v1, v2:= 'Vector'(2) $ 2;

or

v1,v2:= seq(Vector(2), k= 1..2);