Apparently, problems with the default editor take place after you update to Joomla 1.5.14; or when you do a fresh 1.5.14 install. I’ve found a solution to this, that – at least for me – works.
*NOTE I noticed that many people tried to visit my “solution”, but the blog I linked to is a goner. If you’ve got problem with TinyMCE or Joomla 1.514 I’ve got two pieces of advice for you:
1) Install JCE instead of TinyMCE.
2) Update your Joomla! site, people! 1.5.14 is 6 versions old. Get the new version here: http://www.joomla.org