That's interesting, I didn't know that. I think I might be shooting myself in the foot by saving a session and doing "vim -S" to load it again with expandtab set or something. I load multiple buffers associated with a project and use :b to move from file to file. I know it expands the tab when I move to the Makefile buffer, because I have to kick myself and remember to set noexpandtab when it inevitably puts in spaces. Or maybe putting expandtab in my .vimrc overrides the normal behavior.