OpenShift V3 and incremental builds - openshift

Question

I have some issues using incremental builds with the image ruby-22-centos7.
I added the following script "save-artifacts" to .sti/bin directory :
#!/bin/sh -e
pushd ${HOME} >/dev/null
if [ -d ./bundle/ruby ]; then
tar cf - bundle/ruby
fi
popd >/dev/null
I have this error during the build steps :
I0330 13:53:05.022524 1 sti.go:213] Using assemble from image:///usr/libexec/s2i
15 I0330 13:53:05.022544 1 sti.go:213] Using run from image:///usr/libexec/s2i
16 I0330 13:53:05.022551 1 sti.go:213] Using save-artifacts from upload/src/.sti/bin
17 I0330 13:53:05.024552 1 sti.go:142] Existing image for tag 172.30.22.77:5000/blog/blog:latest detected for incremental build
18 I0330 13:53:05.024570 1 sti.go:147] Performing source build from file:///tmp/s2i-build462497527/upload/src
19 I0330 13:53:05.024654 1 sti.go:350] Saving build artifacts from image 172.30.22.77:5000/blog/blog:latest to path /tmp/s2i-build462497527/upload/artifacts
20 I0330 13:53:05.026788 1 docker.go:374] Both scripts and untarred source will be placed in '/tmp'
21 I0330 13:53:05.026820 1 docker.go:510] Creating container using config: {Hostname: Domainname: User: Memory:0 MemorySwap:0 CPUShares:0 CPUSet: AttachStdin:false AttachStdout:true AttachStderr:false PortSpecs:[] ExposedPorts:map[] Tty:false OpenStdin:false StdinOnce:false Env:[] Cmd:[/tmp/scripts/save-artifacts] DNS:[] Image:172.30.22.77:5000/blog/blog:latest Volumes:map[] VolumeDriver: VolumesFrom: WorkingDir: MacAddress: Entrypoint:[] NetworkDisabled:false SecurityOpts:[] OnBuild:[] Mounts:[] Labels:map[]}
22 I0330 13:53:05.685226 1 docker.go:524] Attaching to container
23 I0330 13:53:05.686542 1 docker.go:530] Starting container
24 E0330 13:53:10.836202 1 tar.go:207] Error reading next tar header: io: read/write on closed pipe
25 W0330 13:53:10.859154 1 sti.go:150] Clean build will be performed because of error saving previous build artifacts
26 I0330 13:53:10.859172 1 sti.go:152] ERROR: timeout waiting for tar stream
Any help would be greatly appreciated !