Here is one possible solution, hope it helps (maybe the similar solution is mentionned somewhere else too).
It was written that the problem is with the input, so you must change the input text before posting the form. The thing is that the special characters must be converted into HTML entities (I am not sure if it is necessary to check "enable HTML in descriptions" but I have it checked). For the conversion you can use some online service (ie. http://textmod.pavucina.com/prevod-html-entity). And then you paste the converted result instead of the normal readable text and that is it.