When I click on a sent email SuiteCRM opens the incoming email with the same UID. This seems to be an old issue and was supposedly resolved (#3646). However I am running 7.10.7 and still getting the problem.
Maybe you can simply post on that Issue on Github and explain your experience, and ask for the bug to be re-opened.
All fixed in the 7.10.9 release that came out yesterday !! 