This is strange. Can you please tell me your OS details? Also does the same issue exists with older PSE versions as well?
As a workaorund you can try this:
1. Create an album with all images you want to export. You can easily add media to the album by simply drag drop.
2. Select this album from left panel (so that only media to be exported is seen). Press ctrl+A to select all media.
3. Click on File->Export and try exporting.
Please let me know if it doesn't work for you.
~Surendra