/var is limited in what it can calculate. Anything it cannot calculate is treated as text. That's a limitation, not a bug. 12 % 0 isn't calculating incorrectly in /var... it's just being treated as text because /var doesn't support % in the calculation. It's the same as the example I showed with 1 + 2 + 3, where it would set the variable to that instead of to 6.
A bug is something that is not working as intended. Since /var is working as intended (i.e. it has very basic math support, but % isn't supported), then it's not a bug regardless if you think it should support that. As said, if you think % should be supported in /var, then it's a feature request to expand what /var can handle mathematically. It isn't as if /var is performing some incorrect calculation that is different than $calc()... it just isn't performing any calculation at all and treating it as text. That's simply how /var is supposed to work... if it doesn't think it's a basic math operation, then it treats it as text (i.e. it's working as intended).
