Unwanted doubling of line spacing

Dear Drupal community

I'm experiencing a really annoying problem with TinyMCE. I post content into my nodes by copying and pasting preformatted text from Word. This works fine when I first save a node, but if I go back to edit it later, the spacing between the paragraphs and headings have doubled. It seems something is generating unnecessary p and/or br tags in the code when it's opened up for editing.

I've tried turning off all my Input format filters and I've changed the TinyMCE "cleanup & output" settings back and forth a bit, but the problem still remains.

Any ideas?

Thanks

Olle