I'm not sure this is a bug. If the flap deployment system (hydraulic or electric?) is a single system that deploys both flaps together, then I could see how damage to one of the flaps might jam the mechanism, preventing operation of the other flap.
In general we have a simplistic visual depiction of control surface damage - the damaged item is removed or made invisible. In reality parts of the flap would still be there- torn, twisted jagged metal - a twisted or bent out-of-place piece might easily jam a mechanism.
We do have at least one plane with really great visual damage depiction - the P-39. When rudder, ailerons, of elevators are damaged the piece is replaced with a damaged version, showing the twisted metal and underlying structure. Really cool looking. I don't think I've received flap damage in the '39 though, so I don't know how that is depicted.