ZF-6764: Minor misconception in Zend_Validate messages processing
According to existing documentation getMessages() method returns a list of validation failure messages as => pairs.
It's declared, that getErrors() value can be also get calling array_keys() on the return value from getMessages().
But different validators in the validator chain may have the same message keys, so some messages may be lost.
It also produces problems in Zend_Filter_Input, which uses validators conception for messages processing. All rule validation errors messages are stored within one array.