Question:

Why are Products in a Call Discussion disappearing after saving and then editing a Call?

Answer:

Discussed Products and Discussion Topics are saved on the Call2_Discussion_vod object, on a record related to a Call. Product discussion Details are saved in subsections of the Call Discussion area on the Call, with details of Discussion Topics and the related Products recorded in picklists.

If the Products being discussed are part of a product Detail Group, users must have Read and Edit access to the Detail_Group_vod__c field on the Call2_Discussion_vod object. 

Otherwise, the Products on the Call Discussion subsection will not be saved, and will be erased if the user reopens the Call to Edit it. 

Related Documentation:

CRM Help Documentation: Capturing Product Discussions on the Call Report