GLDEBIT and GLCREDIT Function in Issuing and Returning items

Answer

From the Issues/Transfers application, if a client performs an Issue to someone, and use the GL Debit = 222-2222 and GL Credit = 111-1111, then if they perform a return on that same transaction it automatically fills the GL Debit = 222-2222 and GL Credit = 111-1111.

How does Maximo calculate these transactions and what is its logic behind it?

The MATUSETRANS table is used to record material use transactions. These transactions occur when an item(s) is issued out from a storeroom to a charging entity (work order, location, asset, GL). When an issue is recorded, a credit is made to the storeroom's GL account and a debit is placed on the charging entity's GL. If a return needs to be made for parts that are not used, MAXIMO needs to record a reversal of the transaction. There are two ways to handle this, one is to write the same transaction again, but reverse the accounts, and the other is to keep the accounts the same, but have a negative transaction value. From an accounting standpoint BOTH are financially correct.
MAXIMO 3.x and 4.x originally did NOT employ the "flip-flopping" approach of transaction
returns in MATUSETRANS.

Ultimately for various reasons the "flip-flop" functionality was employed in Maximo 5.
Maximo 5 originally employed the "flip-flopping" approach of transaction returns in MATUSETRANS. However, given the number of issues that have been reported against MATUSETRANS in Maximo 5, the decision was made to revert the functionality back to the way it operated in 4.x (the sign of the linecost will change based on the type of transaction, and the GL accounts will never swap). The code was modified such that the return transaction would be written with a change of the sign for the
linecost and the GL account values would remain the same. Maximo will change the linecost but not the gl accounts for the return transactions.