Within the template ploneglossary_portlet you are using this way for writing open and close span-tags:
<span class="portletTopLeft" />
<span i18n:translate="heading_related_terms">Related terms</span>
<span class="portletTopRight" />
Dont know why, but the IE-Browser needs this way for an correct representation of the portlet:
<span class="portletTopLeft"></span>
<span i18n:translate="heading_related_terms">Related terms</span>
<span class="portletTopRight"></span>
screenshot of our testsite