When creates trigger prototype you may call "Expression constructor" and push "Test" link which will open popup window (which screen shot attached to this report). In this popup windows zabbix web interface shows follow errors:

llegal string offset 'value_type' [tr_testexpr.php:77]
Illegal string offset 'validation' [tr_testexpr.php:79]
Illegal string offset 'type' [tr_testexpr.php:95]

If you need additional details from me please request it.