you will gain muscle in your legs, even if you lose fat. muscle is replacing the fat, and muscle is heavier than fat.
also, depending hw you work out your legs makes a difference.
Doing 6-8 reps in a set is considered mass building because it`s done with heavy weights, yet doesnt burn much fat.
doing 12-16 reps in a set is considered toning and burns more fat than mass building and done with lighter weights.
Doing an exercise for a period of time is endurance, mainly.
Basics, but also to be midful of. Your body type has a lot to do with it as well.
Don`t forget that water weight can fool the scal & make you believe you are heavier when you arent. Hpe this helps.