For what it is worth: you can prevent this from happening by using either the -n or the (as yet undocumented) -p switch to /var. For example, the following code excerpt:
var -n %test = 1 - 1
echo -ag %test
..will echo "1 - 1". The exact same applies in cases where the input is not literal (e.g. when assigning one variable to another, with such a "formula" as contents).