In older versions of source tree, under Windows, I could select a file in the 'unstaged files' listbox and press spacebar to stage that file.
When I updated to 1.8.0 this seemed to have disappeared – now only "CTRL+SHIFT+PLUS" does it, which is ... considerably more verbose. Also recently updated to 1.8.2 hoping it was fixed but no dice.
It would be really great if the spacebar worked for staging files.