Reason code at Document entry

Hi

We have few customer open items (invoices/credit memos etc) and payments items in the system. These documents have text field (BSEG-SGTXT) with some text written by users. But when users are going into document and trying to enter/change Reason code at additional data level, the name of reason code is overwriting the SGTXT field by deleting existing text.

I tried to find any settings in config and substitution rules etc but couldnt find anything. Is there a setting in SPRO to check this or is this a standard SAP functionality? I couldnot find any documentation as well if it is a standard SAP functionality.

Any help would be appreciated.

Thanks