Right indent is not the same as tab

When using Command-] to indent, I get an error in HAML files because it is not the same as indenting with tabs. I have set all my indents (Ruby, Haml, Css, etc) to use tabs, yet it seems that command-] uses spaces. Is there a way to fix this?

Also, I there are times when the right indent command will simply not work, what is the criteria for that?

Thanks.