If your input_forms.xml file includes at least one empty <hint> tag (either <hint/> or <hint></hint>), then the XMLUI will insert in an empty XHTML tag corresponding to that empty hint text:
When Internet Explorer encounters one of those empty XHTML tags, it seems to mess up the CSS for all text following it. Normally, the default CSS for "field-help" includes "font-size: 80%". Unfortunately, IE will apply that style to all text which comes after that empty tag. If you end up having multiple empty "field-help" tags on one page, you end up with drastically decreasing text size as the text is decreased by 80% after each empty tag.
Attached is an HTML dump of an example of this problem, provided by Alice Platt on dspace-tech mailing list.