Incorrect. Select the code, click the toolbar button, or press ctrl+k. That either adds 4 spaces or removes, depending on what is selected.
Also most source code in anything but a very trivial app will tend to be “naturally” indented by 4 spaces when pasted. At least, that is what I saw in 4 years of working on Stack Overflow for 40 to 80 hours a week, with thousands of programmers working in dozens of languages. Your mileage may vary.
And just to be clear, the above toolbar behavior I describe is exactly how SO worked from day one and today, too. Not that it can’t be improved, but seems to me programmers were able to figure it out.