When our inventory department realises that the serial numbers of a batch of items is wrong they used the standard function for changing serial numbers that use the posting events SERREN+ and SERREN-.

The posting events have postings that do not balance if grouped by posting event id:

SERREN-

M1 - Credit
M191 - Debit
M3 - Debit

SERREN+

M1 - Debit
M191 - Credit
M3 - Credit.

To me it seems that the M3 posting should not be there.

Has anyone seen this issue?

Any ideas?