This is more of an ArcMap related question, specifically on publishing a web service. Hence why I am moving it from 'Web AppBuilder' and into the 'ArcGIS for Server' forum.
What release of ArcMap are you using? And can you please provide detailed repro steps and screenshots?
This looks to be related to the following issue:
[#ENH-000095154 Allow modifications to a map document’s metadata to update the map service’s Item Description when overwriting a service]
I'm unsure about a time frame when this issue may be addressed. If you'd like, you can log into myEsri and ask that your customer number be added to list of users who have inquired about this issue.