Submitting Form From Another Frame Does Not Run Onsubmit Of That Form

I have two frames. Frame "search" contains a search form specifying
an onsubmit action like so:

<form ...
...
</form>

The other frame contains a <img ... where
the perform_search function is defined as follows:

<script language="JavaScript">
function perform_search() {
var frame = parent.frames.search;
var form = frame.document.forms.mainForm;
form.submit();
}
</script>

Now, when hitting Return in the search form, then foo() is called
fine. But when clicking on the <img ...
in the other frame, foo() is NOT called.

Is expclicitly calling foo() from perform_search() the only way to do
it, or is there a magic incantation that might do what I want?