This problem exists for one administrator user. The site has several administrators but only one exhibits this problem.
On the 'Edit Page' page the 'Publish' panel (that normally contains the 'Update' button) is truncated such that the entire panel below its header is missing. This problem exists only on 'Edit Page' and not 'Edit Post'
Looking at the HTML for the panel I see:
<div id="submitdiv" class="postbox " >
<div id="submitdiv" class="postbox closed" >
This is curious because the 'close' icon is normally inactive for this panel.