Jim
Mixing between Word and OpenOffice is not a good idea - it's much more sensible to stick with one or the other. Microsoft doesn't publish the specification for doc files - in fact, a doc file is just a memory dump of what MS Word had in memory - and AOO's .doc import had to be reverse engineered.
My guess is that the odt file is somehow slightly wrong in one of the style files suggesting this may happen again. I don't know any html or css coding to suggest how to fix it.
The good news is the style files only tell AOO how to display the text, tables, bullets, pictures etc, but they don't affect the actual document content which is stored elsewhere in the odt file. This is what a typicalodt file looks like when unzipped - the text is stored in content.xml, images are stored in Pictures, etc.

- unzipped typical odt file
I have just done a (very drastic) test. I created a minimum document with just one word in it, and saved it as minimum.odt, so it had very little styles information stored in the odt file. I then created another, more complex document with lots of different fonts, headings, tables, images, indents, paragraph styles etc, and saved it as complex.odt. It had much more styles information stored in the odt file.
I then did "open heart surgery". I copied the content.xml file from complex.odt and inserted it into minimum.odt. I then opened minimum.odt. It now had the complex.odt words in it, and some (but surprisingly not all ) of the formatting was lost. The images weren't there. But no text was missing.
So, in extremis, you could try this.
Be sure to do it on a spare copy, and not on your only version, in case it goes pear-shaped. Ideally you would use the latest "known to be good" odt file (ie before you did the pagination, or the saved by email version) for the "minimum" file so that you kept as much formatting as possible; and your latest "corrupted" odt for the content.xml. Alternatively, create a "minimum.odt" file as I did, but be prepared for more formatting work.
But it is drastic ...
I just had a thought - I wonder if the reason that the saved by email version is OK is because you had deleted whatever it was in the document using the "faulty style", so that faulty style was itself deleted from the saved style data in the sub document. I repeat that I don't know any html or css coding so could be way off beam.