In this situation, when I press enter, I would expect leading spaces to be added to the new line. But when I do, tabs are added instead:

Additionally, when I press the tab key, it adds tabs, not spaces.

Here are my preferences - the relevant part from config.cson:

editor:
    showInvisibles: true
    showIndentGuide: true
    preferredLineLength: 100
    tabLength: 4
    invisibles: {}
    fontSize: 12

And a part of preferences screen (just in case): https://www.dropbox.com/s/vj64h58mg43dsr8/Screenshot%202015-02-11%2012.06.26.png?dl=0

I'm using Atom 0.177.0.