Duplicates not exported
When exporting an image and its duplicate you only get 1 exported image (instead of 2).
Accordingly when exporting an image and its two duplicates there only appear 2 instead of 3 exported images.
Reproducible as follows:
Edit an image. Duplicate it. Edit the duplicate. Select both versions of the image in lighttable mode and try to export them. Messages shows "exporting 2 images". However only one of the two image versions gets exported.