fatal error on membership renewal with REALLY long receipt text

We are seeing an error when a membership is renewed (backoffice) with a really long receipt text entered.

The really odd thing is that the receipt text for the membership type is being altered based on what is being entered in the renewal form - this has been happening since svn but I can't think of a good reason for it - it seems to invite data mis-writes.

Aug 04 16:00:11 [info] $Fatal Error Details = Array
(
[callback] => Array
(
[0] => CRM_Core_Error
[1] => handle
)

[code] => a515ac9c2796ca0e23adbe92c68fc9fc
[message] => DB Error: a515ac9c2796ca0e23adbe92c68fc9fc
[mode] => 16
[debug_info] => UPDATE civicrm_membership_type SET receipt_text_renewal = 'really long receipt text (more than 255 char)' WHERE ( civicrm_membership_type.id = 15 ) [nativecode=1406 ** Data too long for column 'receipt_text_renewal' at row 1]
[type] => DB_Error
[user_info] => UPDATE civicrm_membership_type SET receipt_text_renewal = 'really long receipt text (more than 255 char)' WHERE ( civicrm_membership_type.id = 15 ) [nativecode=1406 ** Data too long for column 'receipt_text_renewal' at row 1]
[to_string] => [db_error: message="DB Error: a515ac9c2796ca0e23adbe92c68fc9fc" code=0 mode=callback callback=CRM_Core_Error::handle prefix="" info="really long receipt text (more than 255 char)' WHERE ( civicrm_membership_type.id = 15 ) [nativecode=1406 ** Data too long for column 'receipt_text_renewal' at row 1]"]
)

Aug 04 16:00:11 [info] $backTrace = #0 /var/www/mysite/sites/all/modules/civicrm/CRM/Core/Error.php(197): CRM_Core_Error::backtrace("backTrace", TRUE)
#1 [internal function](): CRM_Core_Error::handle(Object(DB_Error))
#2 /var/www/mysite/sites/all/modules/civicrm/packages/PEAR.php(931): call_user_func((Array:2), Object(DB_Error))
#3 /var/www/mysite/sites/all/modules/civicrm/packages/DB.php(972): PEAR_Error->PEAR_Error("DB Error: a515ac9c2796ca0e23adbe92c68fc9fc", "a515ac9c2796ca0e23adbe92c68fc9fc", 16, (Array:2), "UPDATE civicrm_membership_type SET receipt_text_renewal = 'Thank you for yo...")
#4 /var/www/mysite/sites/all/modules/civicrm/packages/PEAR.php(564): DB_Error->DB_Error("a515ac9c2796ca0e23adbe92c68fc9fc", 16, (Array:2), "UPDATE civicrm_membership_type SET receipt_text_renewal = 'Thank you for yo...")
#5 /var/www/mysite/sites/all/modules/civicrm/packages/DB/common.php(1905): PEAR->raiseError(NULL, "a515ac9c2796ca0e23adbe92c68fc9fc", NULL, NULL, "UPDATE civicrm_membership_type SET receipt_text_renewal = 'Thank you for yo...", "DB_Error", TRUE)
#6 /var/www/mysite/sites/all/modules/civicrm/packages/DB/mysql.php(898): DB_common->raiseError("a515ac9c2796ca0e23adbe92c68fc9fc", NULL, NULL, NULL, "1406 ** Data too long for column 'receipt_text_renewal' at row 1")
#7 /var/www/mysite/sites/all/modules/civicrm/packages/DB/mysql.php(327): DB_mysql->mysqlRaiseError()
#8 /var/www/mysite/sites/all/modules/civicrm/packages/DB/common.php(1216): DB_mysql->simpleQuery("UPDATE civicrm_membership_type SET receipt_text_renewal = 'Thank you for yo...")
#9 /var/www/mysite/sites/all/modules/civicrm/packages/DB/DataObject.php(2434): DB_common->query("UPDATE civicrm_membership_type SET receipt_text_renewal = 'Thank you for yo...")
#10 /var/www/mysite/sites/all/modules/civicrm/packages/DB/DataObject.php(1337): DB_DataObject->_query("UPDATE civicrm_membership_type SET receipt_text_renewal = 'Thank you for yo...")
#11 /var/www/mysite/sites/all/modules/civicrm/CRM/Core/DAO.php(275): DB_DataObject->update()
#12 /var/www/mysite/sites/all/modules/civicrm/CRM/Core/DAO.php(791): CRM_Core_DAO->save()
#13 /var/www/mysite/sites/all/modules/civicrm/CRM/Member/Form/MembershipRenewal.php(798): CRM_Core_DAO::setFieldValue("CRM_Member_DAO_MembershipType", "15", "receipt_text_renewal", "really long receipt text (more than 255 char)...")
#14 /var/www/mysite/sites/all/modules/civicrm/CRM/Core/Form.php(261): CRM_Member_Form_MembershipRenewal->postProcess()
#15 /var/www/mysite/sites/all/modules/civicrm/CRM/Core/QuickForm/Action/Upload.php(151): CRM_Core_Form->mainProcess()
#16 /var/www/mysite/sites/all/modules/civicrm/CRM/Core/QuickForm/Action/Upload.php(128): CRM_Core_QuickForm_Action_Upload->realPerform(Object(CRM_Member_Form_MembershipRenewal), "upload")
#17 /var/www/mysite/sites/all/modules/civicrm/packages/HTML/QuickForm/Controller.php(203): CRM_Core_QuickForm_Action_Upload->perform(Object(CRM_Member_Form_MembershipRenewal), "upload")
#18 /var/www/mysite/sites/all/modules/civicrm/packages/HTML/QuickForm/Page.php(103): HTML_QuickForm_Controller->handle(Object(CRM_Member_Form_MembershipRenewal), "upload")
#19 /var/www/mysite/sites/all/modules/civicrm/CRM/Core/Controller.php(339): HTML_QuickForm_Page->handle("upload")
#20 /var/www/mysite/sites/all/modules/civicrm/CRM/Member/Page/Tab.php(251): CRM_Core_Controller->run()
#21 /var/www/mysite/sites/all/modules/civicrm/CRM/Member/Page/Tab.php(316): CRM_Member_Page_Tab->edit()
#22 /var/www/mysite/sites/all/modules/civicrm/CRM/Core/Invoke.php(323): CRM_Member_Page_Tab->run((Array:4), NULL)
#23 /var/www/mysite/sites/all/modules/civicrm/CRM/Core/Invoke.php(72): CRM_Core_Invoke::runItem((Array:14))
#24 /var/www/mysite/sites/all/modules/civicrm/CRM/Core/Invoke.php(52): CRM_Core_Invoke::_invoke((Array:4))
#25 /var/www/mysite/sites/all/modules/civicrm/drupal/civicrm.module(405): CRM_Core_Invoke::invoke((Array:4))
#26 [internal function](): civicrm_invoke("contact", "view", "membership")
#27 /var/www/mysite/includes/menu.inc(350): call_user_func_array("civicrm_invoke", (Array:3))
#28 /var/www/mysite/index.php(17): menu_execute_active_handler()
#29