"Strapping" or applying a jumper from line to load sides of the meter, creates a parrallel path for the current flow, part going thru the meter & part of it thru the strap or jumper. This is illegal & an unsafe practice... In Massachusetts the utilities are allowed to estimate the stolen energy & bill for triple the cost.
As for the meter running backwards with no load. This is creep & the disk should only roll back a patial revolution, until the anti-creep holes react with the retarding magnets & stop the disk. If the meter creeps backwards ir usually means the meter is slow under a light load, & if it creeps forward it is usually fast under light loads. Most utilities calibrate mechanical electric meters to be within + or - 0.5%. I have tested 50 - 60 years old meters that were still within this accuracy window.