[Zope] Size limit on Zclass text property???

Hi, I need urgent help! I created a ZClass with 5 string properties and 2 text properties. When I try to add an instance containing more than (circa) 1500 characters on one of the text properties (or on both summed), I get an error like "no value for propertyname...". If I add an instance and try to change its text properties to hold more than 1500 chars, it simply cuts the content up to (circa) 1500! Is this a classical problem? How can I handle this??? Thanks for the help! Regards, Rogerio