'Event edit' (/eventedit) uses name='t' to identify the 'time' field in form.
'Edit Report Format' (/rptedit?rn=10) uses name='t' to identify the 'title' field in form.

The simplest was to resolve this is to change t to time or title respectively

Note:
I added the following to the header to allow the use of a date picker for the 'Event edit' and the new and edit ticket screens. :

<pre>
<link rel="stylesheet" type="text/css" media="screen">

<script
<script

<script type="text/javascript">
always use datepicker for this field
 $(function() {
  $( "input[name='t']" ).datepicker({
			numberOfMonths: 2,
			showButtonPanel: true,
			dateFormat: 'yy-mm-dd'
		});
  });
</script>

<script type="text/javascript">
    var datefield=document.createElement("input")
    datefield.setAttribute("type", "date")
if (datefield.type!="date"){ browser doesn't support input type="date", initialize date picker widget:
    jQuery(function($){ document.ready
 $( "input[name='last_useful_date']" ).datepicker({dateFormat: 'yy-mm-dd'});
 $( "input[name='date_closed']" ).datepicker({dateFormat: 'yy-mm-dd'});
    })
}
</script>
</pre>