gthumb starts up (with the gtk-CRITICAL assertion messages in bugrep )
which don;t appear to do any particualar harm.

If I select 'import from'->'removable device' it shows the
thumbnails OK (there are 184 files to import). I have 'delete the
imported files from the source' ticked, Other prefs are 'Automatic
subfolder' (by file date, Y-M-D), and 'rotate images pysicaly'.

Importing starts when I click on the 'Import' button, but it
crashes after a random time with
gthumb: tiffcomposite.cpp:1299: virtual uint32_t
Exiv2::Internal::TiffDirectory::doWrite(Exiv2::Internal::IoWrapper&,
Exiv2::ByteOrder, int32_t, uint32_t, uint32_t, uint32_t&): Assertion
sv == d' failed.
Aborted

The same happens if I select just one image to import. If I deslect
'delete the imported files from the source' then it imported one pic
OK. But asserted again when I tried all of them. It seems possible to
import much smaller number of images: 2,20,40. Even if 'delete the
imported files from the source' is selected, so that's a red herring.

Upgrading to the testing version 3:2.13.1-1 (along with gthumb-data,
libpcre3 (8.12-3), and libglib2.0-0 (2.28.6-1) fixes this problem.