Issue when opening html file in Word

When I open a particular HTML file in Word 2007, I'm getting some odd
behavior. The HTML is a letter and all the different letter parts are
formatted as (nesting)HTML tables. When I scroll toward the bottom of the
letter (full letter is about 1.5 screenfuls of data), the text from the
letter ends when there is really more text to go. Then immediately following
this abrupt end, the letter starts over from the top. And if I move my
cursor over the part of the Word window where the letter starts over, that
text disappears. (I kid you not!)

After playing with this for a while, I noticed that when the cursor was
inside the main table that contains the whole letter, the "Repeat Header
Rows" option was selected. I deselected this option and the letter displays
perfectly. It seems that if the HTML table has a THEAD tag, then Word's HTML
renderer sets that row as repeatable. Can anyone confirm this?

Unfortunately I was planning to somehow automate this process to convert a
set of HTML letters to docx files. Using the Open XML packaging and loading
the HTML as an AltChunk part was mind-numbingly easy. But this way the HTML
is saved in the docx file as is and doesn't get rendered until someone opens
the docx. I really want to save the docx in an accurate state. So I could
instead automate Word and open the HTML file -- but is there any way for me
to affect the rendering or will I have to look for tables that have been
created and have "Repeat Header Rows" set?
Any suggestions?