I've fixed this upstream. I'll try and release this as soon as possible. If you are happy patching, the fix is trivial:
diff --git a/bin/gscan2pdf b/bin/gscan2pdf
index 84f1c22..f8b607a 100755
--- a/bin/gscan2pdf
+++ b/bin/gscan2pdf
@@ -3137,7 +3137,7 @@ sub file_chooser_response_callback {
save_djvu( $filename, $list_of_pages );
}
when ('tif') {
- save_tiff( $filename, $list_of_pages );
+ save_tiff( $filename, undef, $list_of_pages );
}
when ('txt') {
save_text( $filename, $list_of_pages );

