I was just about to post the same thing. It was working in the last version (as far as I recall). When I installed the new version after the recent KSP update I can no longer fill stock tanks with just LF/LOX/LF+LOX. It only has the option to change the size of the tank.
I hope this can be resolved as I rely on having a full LF tank on some of my craft (some already in flight).
Cheers!