The entire document contents is on a single line after XHTML export. Such multimillion character lines cause problems with the other software.
Can you please name some of these other software and open bug reports for them.
So report bugs for the other software. It is not our problem that someone is using a crappy XML parser.
*** Bug 89143 has been marked as a duplicate of this bug. ***
Bug 89143 concerns a bug in the HTML save option. It is neither resolved nor a duplicate of this bug.