UPDATE 2016-11-25: SAP has responded regarding the issue and has offered a workaround:
It seems that there is a change in the “Reference Field Links”, that needs to change the definition of the “Remarks – Row” and “Remarks – BP Row” to “Not Defined” and then again to “Journal Remarks”.
After that, the update of the journal remark is working again.
We do not know if SAP will fix this, and at this time, only this workaround was provided by SAP Support.
SAP has made a change in how Document Journal remark and Journal Entry Journal Remark synchronize in SAP 9.2 PL5 and higher
You can easily produce this even without the add-on:
1- Create new invoice and write 'abc' in Journal Remark.
2- Add Invoice and see journal entry correctly set is as abc
3- Now update invoice's journal remark to 'qwe' and update
Expected: Journal Remark on journal entry should be 'qwe' (was in older SAP versions)
Actual: Still 'abc' (aka not synchronized anymore)