It seems that framework doesn't pay attention to parameter 'on' value.
Rules:
array('field', 'required','on'=>'RequestA')
If i am validating wtih $Class->validate(‘RequestA’); - it validates ‘field’,
If i am validating with $Class->validate(‘RequestB’); - it validates ‘field’ also,
There are no issue while i am validating like this: $Class->validate();