I also encountered this bug.
I think this might be due to the new behavior in dkms 2.2.1.0 which seems
to remove the build directory.
The postinstall script set in dkms.conf tries to copy files from the build
directory which does not exist.
Changing the phase that the copy occurs in seems to fix it.
--- usr/src/spl-0.6.5.7/dkms.conf 2016-05-25 15:42:03.000000000 +1000
+++ usr/src/spl-0.6.5.7/dkms.conf.orig 2016-09-09 10:37:43.482388086 +1000
@@ -20,7 +20,7 @@
esac)
--with-linux-obj=${kernel_source_dir}
"
-POST_INSTALL="cp
+POST_BUILD="cp
${dkms_tree}/${PACKAGE_NAME}/${PACKAGE_VERSION}/build/spl_config.h
${dkms_tree}/${PACKAGE_NAME}/${PACKAGE_VERSION}/build/module/Module.symvers
${dkms_tree}/${PACKAGE_NAME}/${PACKAGE_VERSION}/${kernelver}/${arch}/
