Warehouse journal entries One and /two in item journal


please can you help me to analyze this case :

i need to make ware house adjustment entries for example -ve -48.2

step 1 to go to warehouse item journal and and enter negative line for -48

step 2 register the warehouse entries

step 3 go to item journal to post the entries on level of item journal

in step three in item journals you willl see two lines

one line postive 36

2nd line negative -84.2

Why do we have two line coming from one line . As i need to know why the system is separating the one line from warehouse entries into two lines in item journal.

i facing here problem because if i dont have from this enough negative quantiy of specif Lot and i couldn’t post it .

thank you

appreciated help