What are these "leading" lines in vim?
 

http://imgur.com/al5huJs

I only see them occasionally, and I'm just wondering what they are.

I think those are DOS carrier returns.

Those can greatly disrupt UNIX test files, so you'll want to try to get rid of them. dos2unix works, as does other editors that support UNIX text file creation and editing.

They could be 'tabs'

See if you have

In ~/.vimrc or /etc/vim/vimrc

could use cat -A to confirm