How I got CKEditor to work with Geshi in Drupal 7
This is a quick post. I've just spent hours getting Geshi to properly format special characters. Namely "<" and ">" being the most annoying.
You see when you have ckeditor installed it encodes special characters into HTML. So you end up with "<" and ">". Rather annoying if you want to display a snippet of code in a useful way.
After lots of the usual soul searching We found the patch that resolves this issue. It requires that you install the dev release. After installing that and applying the patch you have to visit this page /admin/config/content/formats/geshifilter and tick the checkbox for "Decode entities".
After doing this Geshi is working as expected.