Problem description:
Some Microsoft Word 97-2003 format documents make LibreOffice very sluggish, particularly when scrolling. On saving these documents to ODT, I find hundreds of redundant style tags.

Steps to reproduce:
I have some documents which have been edited by several authors using  LibreOffice and various versions of Microsoft Word (e.g. Word 97 and Word 2010). The documents open normally in Microsoft Word 97 but cause problems for LibreOffice. When I save them as .ODT and unzip them to look at the content.xml file, I find that there are redundant style tags between almost all pairs of words.
These documents are confidential so I cannot attach them, and I have been unable to reproduce this problem in a new document. These tags might have been inserted by Microsoft Word, but LibreOffice should be able to detect and remove redundant style tags. I was able to remove these tags by cutting and pasting as HTML into a new document.
I don't recall that this was a problem in LibreOffice 3.4.0, but I have uninstalled it so I cannot do a direct comparison.

Current behavior: (fragment of content.xml file with unnecessary style tags):
<text:span text:style-name="T2"></text:span>
recognise
<text:span text:style-name="T2"></text:span>
the
<text:span text:style-name="T2"></text:span>
context
<text:span text:style-name="T2"></text:span>
of
<text:span text:style-name="T2"></text:span>
diagnoses
<text:span text:style-name="T2"></text:span>
in
<text:span text:style-name="T2"></text:span>
the
<text:span text:style-name="T2"></text:span>
text.
<text:span text:style-name="T2">I</text:span>
t

Definition of style T2 in content.xml: 
<style:style style:name="T2" style:family="text">
<style:text-properties style:font-name-asian="Times New Roman"/>
</style:style>

Expected behavior: (expected no formatting in this fragment of text)
recognise the context of diagnoses in the text. It

Platform (if different from the browser): Ubuntu 12.04
              
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