With the new 'Manage Files' button in both ATTO and TinyMCE I found that there was no submit / insert button, so could could upload a file but actually do nothing with it. When returning to the dialog all you can do is delete the file that you've uploaded. So, I created MDL-50302 as a bug which has now been transformed into an enhancement for a message to be displayed. I don't believe that this is the correct solution and indeed its still a 'bug'. I have been 'advised' that this now needs to be discussed in the forums.
Therefore please do have a look at MDL-50302 and say what you think here.