Partial breakage in the Open University ruleset
Report 1:
https://mail1.eff.org/pipermail/https-everywhere-rules/2011-August/000578.html
Report 2:
Concerning the HTTPS rule for the Open University:
If it is enabled, the interactive forums (VLE), where the discussion of the study content takes place, can no longer be accessed.
After disabling the predefined rule of HTTPS Everywhere via its context menu, everything worked fine again.