[validation] Submit button value disappears

[validation] Submit button value disappears

Hi,
 
We have another problem with validation pluggin that shows erratic behaviour. Depending on some fields beeing filled or not, the SUBMIT button value is not passed (or is lost somewhere).
 
I suspect the AJAX validation of fields that is a post to a PHP script and interferes with the final POST. The submit buttons (we have 2 and need to get their values) do not transmit their values. Firebug analysis shows all POST fields except SUBMIT. 
 
We see that on a form that have all fields filled, then SUBMIT values are passed, but if incomplete fields are posted, SUBMIT values are not passed.
 
Someone would have an ideia where to look to understand why this happens?
 
thanks
Pierre