February always comes out as March - expect /yyyy/mm to be 2018/02 but it's 2018/03
I think the problem is that you are not being specific enough with the date that you are passing to the date function. You are in effect calling date("February") and the PHP date function has to make an assumption and uses the current day of the month, i.e. February 30 which equates to March. If this is correct you will have even more issues tomorrow being the 31st!

If you make the date being passed more specific i.e. February 1 it should work fine.

A related PHP bug post, that wasn't a bug, explains it https://bugs.php.net/bug.php?id=49115