One of my users created deals and wanted to add a task, set a meeting and start an email to attach to the deal. Clicking on the links within a deal to do these things opens a window to create an item but when he clicks 'Save' the deal shows no recent activity.
I'm trying to reproduce the issue in my lab according to your description, but I get stuck during the process. Could you please provide more detailed information about "start an email to attach to the deal." ? Do you mean save an email as msg file and add this msg file to this deal? Some screenshots about the steps will be better to understand the scenario.