Storing some text containing some special characters (like "&") is not possible in an eZmatrix attribute.

Indeed, it seems that the text content has just to be washed on attribute storing (because of XML), the simple attached patch, basically a htmlspecialchars, fixes the problem by transforming HTML values before its storage.

Steps to reproduce

• Edit a class and add an eZmatrix attribute to this class
• Create an object of this class, then fill information
  In the eZmatrix attribute, type a text containing some special characters as can be "&".
  For an example, try to storie an urls containg get variables, it will end in a text like "http://www.somesite.com/page?var=yes&var2=no&var3=rulez"
• Publish the content

Reopen your content, you should then see that your string has been broken, only the text before the "&" has been kept, the rest has been lost.