/var is working as intended (i.e. it has very basic math support, but % isn't supported)
% is supported in /var:
%x becomes 2 in the above statement. That is what I call "support". The fact that it doesn't work properly for all inputs (namely 0) doesn't mean it's "not supported", that means it's a bug.
Common sense would dictate that if A % B works in /var, you should expect A % B to function as it does in $calc. Otherwise you have inconsistent behaviour ($calc does X, /var does Y) which by definition defies standard expectations. Therefore A % 0 does not do what someone would reasonably expect it to.
