How Credit memo accounting string is derived when it is created on top of transaction?

Summary:

In this scenario where a total of 3 receivable lines are coming up while accounting, wanted to understand how those extra receivable lies are deriving the Accounting GL String.

In the above scenario, the actual invoice Receivables line is having GL string similar to the line no. 3, so line no. 3 having that GL string making sense, but the GL string for line 2 nd 4 is totally unexpected.

So, wanted to understand the actual logic behind the GL code derivation for these offset receivable lines in these scenario.
Thanks.

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