QuickForm problem with hidden fields

Hi there, I've a Quickform with two selectboxes. After submitting I want to test, which of the selectboxes have different values compared to the state before submiting. So I thought the solution is to add hidden fields with the transmitted values from the selectboxes. But this only works for the first time (as the value in the hidden field is always set to the first submited value). Do you have a solution where the above scenario works for as many submissions as I want?? Thanks in advance Patrick