My question is : What is the cause of this problem? Does gimp and others uses hard-linked libraries and ld.so.conf is for nothing??
Yes.
$ eu-readelf -d /usr/bin/gimp | grep PATH RPATH Library rpath: [/usr/lib64] $
I think there is some packager maintainers' page about eliminating bogus RPATH from package builds, but I don't have the pointer off hand. The package maintainer for gimp needs to be pointed at that.
Thanks, Roland