For me, on Win 7 things are stranger still. Typing does not happen at the cursor position but some arbitrary (and varying) number of spaces away. E.g., if you try typing at the end of a comment line, the letters appear inserted in the middle of the existing comment instead.
This is in the editor that open when I double-click a js object.
We have been trying to track this issue down for a while now and have been unable to reproduce. It may be due to some font issues. What default fonts do you have in Max Preferences? What language does your OS use?