not sure what you expect in addition to a clear guidance given by SAP in the mentioned OSS note.
the note says that the stock is not checked in the posting routine, it is only checked when you enter the document.
this means if you had a posting failure, and the user did the posting again without any failure,and then the posting failure was processed as well, then it will cause this situation.
or
if your lock table is full, and the posting is hanging there and has not yet updated the database, and the user enters it again SAP has still the old stock situation, hence it will allow this double posting, then you have 2 entries in the lock table. When this lock situation is cleared, both documents will be posted and hence create this negative stock situation.
The path how to clear this negative stock is given in the note.