I (the author) also get this with my HP OfficeJet 6500.
Pressing cancel ejects the page, so I don't have to pull it out.
Alternatively, exiting gscan2pdf should also eject the page.
For some reason HPLIP doesn't eject the last page from the ADF until
the complete interface is closed.
I played with closing the interface after every scan job, but that
caused other problems, so I put up with hitting the cancel button, or
waiting until I exited gscan2pdf.
If you don't need the extra functionality of the libsane-perl
frontend, switch back to the scanimage frontend in Edit/Preferences.
That also fixes this problem.
I (the author) also get this with my HP OfficeJet 6500.
Pressing cancel ejects the page, so I don't have to pull it out.
Alternatively, exiting gscan2pdf should also eject the page.
For some reason HPLIP doesn't eject the last page from the ADF until
the complete interface is closed.
I played with closing the interface after every scan job, but that
caused other problems, so I put up with hitting the cancel button, or
waiting until I exited gscan2pdf.
If you don't need the extra functionality of the libsane-perl
frontend, switch back to the scanimage frontend in Edit/Preferences.
That also fixes this problem.