Stash should work similar to Commit - the selection should define whether to stash all or just the selection
Not selecting any file, both cmd + k and cmd + s commits, respectively stashes all the files in the working tree.
Selecting one or more files from the working tree, cmd + k commits them while cmd + s stashes all the files, in which case the selection is completely ignored.
This is not consistent and, at least for me, very unintuitive. A lot of times I selected some files, hit cmd + s, and pressed enter, only to see that all the files were stashes instead.
Customer support service by UserEcho