Do any code editors also treat a delete of one of these spaces as removing the tab width size? (I've never seen it, but maybe there are ones that do that.) What tends to happen is that yes, the tab enters the N spaces, but if you have to move code around, you can find yourself deleting a lot of spaces.
You are right, it looks like it tries to do the right thing on indent. Though if you try and use tabs to align anything after an indent it just treats them as spaces.
