Today I noticed (after getting symfony from svn), that id attribute for fields in generated admin don't match these given to calendar's configuration, e.g. I have a field addtime, and it's generated to:
<input type="text" name="news[addtime]" id="news_addtime" value="" withtime="1" calendar_button_img="/sf/images/sf_admin/date.png" size="9" /><img id="trigger_news[addtime]" style="cursor: pointer; vertical-align: middle" src="/web/sf/images/sf_admin/date.png" alt="Date" /><script type="text/javascript">
document.getElementById("trigger_news[addtime]").disabled = false;
Calendar.setup({
inputField : "news[addtime]",
ifFormat : "%Y-%m-%d",
button : "trigger_news[addtime]"
});
</script>
As for now calendar uses getElementbyId, so it's completely broken in this case.