Hello,
indeed, this is a bit strange. Although OpenOffice in combination with PDF2SWF is known to not produce the same results when converting Office documents as the Microsoft products give, I have not yet seen something like in your case - usually, you have a proper page format and content is just not visible, not some overlay that exceeds the page boundaries.
Have you checked the intermediary PDF or generated SWF as well? It would be good to know in what part of the transformation and display chain this artifact is produced. You can check the PDF by doing a straight conversion with Alfresco via the "Run Action" feature. The SWF you can inspect via the Node Browser as content of the "preview" rendition node for the document in question.
Regards
Axel