I'll Fix It - S4-E2
Continuity mistake: When Station 51 is at the scene of the oil well eruption, underneath a house which was built atop an abandoned oil field, just after Johnny tells Roy that he thinks the whole foundation is slipping, it cuts to a shot of the front porch as one of the porch columns (and part of another) breaks and falls. However, when the guys finally free the trapped man and carry him out, all the columns are upright once again.