We are currently evaluate this issue and are working towards a resolution.

Workaround
  1. Do not delete the source constituent when merging in the database view
  2. Manually add the web view specific data to the new constituent record
  3. Delete the source constituent record
Please see the list below of fields that do not automatically merge in the web view:

 
Field name (from the UI)DescriptionFeature/Area
AttachmentsConverted  media from constituent records from the database view and all attachments on constituent records in the web view Constituent Attachments, Action Attachments, Gift Attachments
Prospect status history – Start dateThe date of a prospect status changeProspect status history in Prospect management tile on Constituent page
Prospect status history – CommentsUser comments associated with a prospect status changeProspect status history in Prospect management tile on Constituent page
Opportunity status history – Start dateThe date of a opportunity status changeStatus history tile on opportunity page
Opportunity status history – CommentsUser comments associated with a opportunity status changeStatus history tile on opportunity page