Two document for one movement

Dears

By using Quality Notification Q2 type,in Action box i move my materrial unresticted to block area

now system create two documnet as follows

Movement type :344 and item :1 (moved qty as +)

Movement type :344 and item :2 (moved qty as -)

Why system create two item in one movemnet type

what is the logic behind this

Faisal