look to be javascript error...
Quickly looking in the login.htmpl form the comments tags around the button macro show no compliant use of it and not be interpreted correct by your browser (around line 360).
if the form is OOB then CA to provide patch.
However you can correct your self in the mean time by removing the extra comments in the already commented section. (removing the highlighted below must do the trick)
<script type="text/javascript">
<!--
if (!_browser.supportsLayers &&
_browser.name != "unknown")
{
// Explicitly hide hardcoded button (in case browser doesn't understand noscript)
var e = document.forms["login"].elements["HardcodedSub"];
if ( typeof e == "object" && e != null )
e.style.visibility = "hidden";
<PDM_IF "$prop.WSPHOST" != "">
<PDM_MACRO NAME=button caption="Log In[!Log In]"
hotkey_name="Log In[!Log In]" id="btndflt" width=0
func="parent.form_submitted=true;pdm_submit('login','')">
<PDM_ELSE>
<PDM_MACRO NAME=button caption="Log In[!Log In]"
hotkey_name="Log In[!Log In]" id="btndflt" width=0
func="pdm_submit('login','')">
</PDM_IF>
<!-- Write hidden link to allow screen reader users to set preference -->
document.write('<a href="javascript:loginAndSetScreenReaderPreferences()" tabindex=-1' +
' title="Login and set screen reader preference"><\/a>');
}
//-->
</script>
Hope this help
/J