Hi, I am the upstream author of FabIO and indeed, there is a regression in the tests when run for the first time. This is linked to an un-flushed file. This can simply be corrected with this simple patch https://github.com/silx-kit/fabio/pull/550/files
It is probably simpler to debian to just apply this patch to the source when packaging instead of making a new release... Cheers, -- Jérôme Kieffer tel +33 476 882 445