This is for the Blackbaud plugin for Gmail (I am not sure if it applies to Outlook).

Assume you e-mail a prospect and you save the conversation (all is well on their record). However, if the donor responds back - creating a conversation thread - and this goes back and forth - when you save again, it will create another action on the constituent's account, however, it only shows the initial conversation without the back and forth conversation thread.

I found a solution by renaming the subject line. When renamed, it creates a new action with the most up-to-date conversation exchange. 

Ideally, when the conversation continues with someone for whom an action is created, a new action would not be created and the current conversation would update on the outstanding action.