We're using EPiServer CMS 6 R2. In edit mode when comparing a version with another we get the following error when using the "With Markup" comparison type: Page version comparison does not support redirect on page. Use 'Side by side' to see the page content.
I've checked in Fiddler and there are no redirects. This happens only on certain pages, but there is nothing I can see what can be cause (e.g. no custom properties etc).