FABIOLA (1949)...oops!

Continuity mistake in FABIOLA (1949). Henri Vidal (in light tunic) fights with a gladiator and at first the gladiator's tunic is short but then in the next scene it's long, almost all the way to the knees. But the following scene, the tunic is back to being short. I always wonder how these mistakes happen. I know the scenes might have been shot on different days but wouldn't the costume remain the same?