ADDing file to symlink directory destroys symlink

[cpeel]

Actual behavior
ADDing a file to a directory that is a symlink to another directory destroys the symlink and recreates it as a directory.

Expected behavior
The file is added to the symlink destination rather than destroying the symlink, like docker build does.

To Reproduce
Create a file in the cwd that will be used for the docker context:

touch file

Dockerfile:

FROM phusion/baseimage:0.11
ADD file /etc/service/file

Build:

docker run --rm -it -v $(pwd):/workspace gcr.io/kaniko-project/executor:v0.12.0 \
    /kaniko/executor \
    --context /workspace
    --dockerfile /workspace/Dockerfile \
    --destination $REGISTRY/kaniko-repro

See how in the base container /etc/service is a symlink to /etc/runit/runsvdir/default:

$ docker run --rm -it phusion/baseimage:0.11 ls -l /etc/service
lrwxrwxrwx 1 root root 22 Nov 16  2017 /etc/service -> runit/runsvdir/default

Whereas in the kaniko-built container it's now a directory:

$ docker run --rm -it $REGISTRY/kaniko-repro ls -l /etc | grep service
drwxr-xr-x 2 root root        4096 Sep 16 20:17 service
$ docker run --rm -it $REGISTRY/kaniko-repro ls -l /etc/service
total 0
-rw-r--r-- 1 1000 1000 0 Sep 16 20:17 file

Additional information
docker build does the expected thing of putting the file in the destination symlink.

$ docker build -f Dockerfile -t $REGISTRY/kaniko-repro .
Sending build context to Docker daemon   2.56kB
Step 1/2 : FROM phusion/baseimage:0.11
 ---> 14e6c478b00a
Step 2/2 : ADD file /etc/service/file
 ---> db470ec738eb
Successfully built db470ec738eb
Successfully tagged $REGISTRY/kaniko-repro
$ docker run --rm -it $REGISTRY/kaniko-repro ls -l /etc/service
lrwxrwxrwx 1 root root 22 Nov 16  2017 /etc/service -> runit/runsvdir/default
$ docker run --rm -it $REGISTRY/kaniko-repro ls -lL /etc/service
total 8
drwxr-xr-x 2 root root 4096 Aug 16  2018 cron
-rw-r--r-- 1 root root    0 Sep 16 19:44 file
drwxr-xr-x 2 root root 4096 Aug 16  2018 sshd