(it's have been there for a long time but I didn't found the time to post it)

When I want to delete a file from the repository, I often do it by deleting the file first, then use the Working Copy view to review what I just did and commit the change.

In the commit screen, selecting new files that are not tracked will result in a prompt asking if I want to add them (which I want most of the time).
However, selecting files that have been deleted will result in nothing. Neither prompt nor removed from the repository.

This is problematic because almost each time I want to delete files, I first do a commit, then realize the deleted files that were selected on commit have not been removed from tracking, and there is no prompt telling me so. So I have to do another commit or rollback if I realized it soon enough. (but rollback action isn't visible from SourceTree so each time I have to do it from command line)

(Preferred) Suggestion 1: use a solution similar to TortoiseHg.
In TortoiseHg, selecting untracked files on commit will result in a prompt asking if we really want to add these files - exactly like SourceTree.
However, selecting deleted files on commit will result in another prompt asking if we really want to remove these files - not like SourceTree.
This is "elegant" in that it's a symmetric behavior (if we could say that).
Note that TortoiseHg prompt twice if you have added and deleted files in the same commit (which I do each time I totally remove sources from a dependency and replace it by a new version of this dependency sources). I found it very helpful.

Suggestion 2 (less elegant I think): Don't allow selecting untracked or deleted files for commit if they are not yet associated with a valid action (either add or remove). This would force the user to choose explicitely what to do with these before committing them or let them untracked. I think it might work too but I didn't try it, while the solution used in TortoiseHg always worked very well for me. Maybe this solution is safer though.

I guess we could say Suggestion 1 is "implicit" in that it is assuming that selecting a deleted file for commit means the user wants it removed from tracking (with a prompt to be sure that's what's intended); while Suggestion 2 is "explicit" in that it will allow action on a deleted file until it's either explicitly removed or restored.