Cannot select contact with autocomplete on add/edit activity in IE

Have reproduced this on the demo site:

Load IE (6,7 or 8)

Go to add new activity page:
/civicrm/activity&reset=1&action=add&context=standalone

type a contact name ( E.g. Adams) into the 'With contact box' to start the autocomplete. Click the resulting name; "Adams, Andrew". The name does not appear in the box (nothing happens).

In firefox, clicking the name adds it to the 'With contact' box fine.