Duplicate instance in depot repair

Hi Team,

I find that somehow users where able to use serial numbers which looks same when checked in front end but have different instance number.

Below are the details

SELECT a.description "User", b.last_updated_by,

  b.last_update_date,

  b.source_serial_number,

  b.source_instance_id

FROM csd_product_transactions b,

fnd_user a

WHERE b.repair_line_id IN ( 401048 , 402318)

and a.user_id = b.last_updated_by;

User	LAST_UPDATED_BY	LAST_UPDATE_DATE	SOURCE_SERIAL_NUMBER	SOURCE_INSTANCE_ID
Jayesh Kapadia	37314	27-OCT-16	M53C16001793	46549292
Jason Almeida	38061	07-DEC-16	"M53C16001793 "	47966417

If you see the serial number is somehow created with junk characters and was not intentional I believe but how was this created in first place where the serial number block in both Details and Logistics tab doesnt take junk characters.