Hi GRK,
The only reason this should be occurring is if you have the image turned to OFF in the Media section in the export settings.
Currently there are to media sections, one for the page title and one for the internal pages. This will be merged in an update, but for now you need to go into the media settings for the internal pages (It's the 2nd media option)
If you need any further help, just let us know.
Regards,
Luke