Docker/Quay.io hash weirdness: How did the image ID mutate from 5e0980f79b63 -> 40a52d6ca462?

gistfile1.txt

$ docker -v
Docker version 1.8.3, build f4bf5c7

$ docker pull gliderlabs/logspout:master
$ docker history gliderlabs/logspout:master
IMAGE               CREATED             CREATED BY                                      SIZE                COMMENT
5e0980f79b63        9 weeks ago         /bin/sh -c #(nop) ONBUILD RUN cd /src && ./bu   0 B                 
87d9ab176e8e        9 weeks ago         /bin/sh -c #(nop) ONBUILD COPY ./modules.go /   0 B                 
3a7ba44aa875        9 weeks ago         /bin/sh -c cd /src && ./build.sh "$(cat VERSI   9.621 MB            
baa3d344bd8c        9 weeks ago         /bin/sh -c #(nop) COPY dir:b7de7efabd9eb9bba3   90.86 kB            
c6b6501ca3e2        9 weeks ago         /bin/sh -c #(nop) EXPOSE 8000/tcp               0 B                 
d498fa572b01        9 weeks ago         /bin/sh -c #(nop) VOLUME [/mnt/routes]          0 B                 
5df877c50c17        9 weeks ago         /bin/sh -c #(nop) ENTRYPOINT &{["/bin/logspou   0 B                 
bee15e00f492        5 months ago        /bin/sh -c #(nop) ADD file:ab9e2f3982a65d1cf4   5.041 MB            
d634beec75db        2 years ago                                                         0 B                 Imported from -

$ docker tag gliderlabs/logspout:master quay.io/subledger/logspout:master
$ docker history quay.io/subledger/logspout:master
IMAGE               CREATED             CREATED BY                                      SIZE                COMMENT
5e0980f79b63        9 weeks ago         /bin/sh -c #(nop) ONBUILD RUN cd /src && ./bu   0 B                 
87d9ab176e8e        9 weeks ago         /bin/sh -c #(nop) ONBUILD COPY ./modules.go /   0 B                 
3a7ba44aa875        9 weeks ago         /bin/sh -c cd /src && ./build.sh "$(cat VERSI   9.621 MB            
baa3d344bd8c        9 weeks ago         /bin/sh -c #(nop) COPY dir:b7de7efabd9eb9bba3   90.86 kB            
c6b6501ca3e2        9 weeks ago         /bin/sh -c #(nop) EXPOSE 8000/tcp               0 B                 
d498fa572b01        9 weeks ago         /bin/sh -c #(nop) VOLUME [/mnt/routes]          0 B                 
5df877c50c17        9 weeks ago         /bin/sh -c #(nop) ENTRYPOINT &{["/bin/logspou   0 B                 
bee15e00f492        5 months ago        /bin/sh -c #(nop) ADD file:ab9e2f3982a65d1cf4   5.041 MB            
d634beec75db        2 years ago                                                         0 B                 Imported from -

$ docker push quay.io/subledger/logspout:master
The push refers to a repository [quay.io/subledger/logspout] (len: 1)
Sending image list
Pushing repository quay.io/subledger/logspout (1 tags)
Image d498fa572b01 already pushed, skipping
Image 5df877c50c17 already pushed, skipping
Image c6b6501ca3e2 already pushed, skipping
Image bee15e00f492 already pushed, skipping
Image d634beec75db already pushed, skipping
Image 3a7ba44aa875 already pushed, skipping
Image 5e0980f79b63 already pushed, skipping
Image baa3d344bd8c already pushed, skipping
Image 87d9ab176e8e already pushed, skipping
Pushing tag for rev [5e0980f79b63] on {https://quay.io/v1/repositories/subledger/logspout/tags/master}

View screenshot of quay.io here: http://imgur.com/f0dDZ1N

$ docker rmi quay.io/subledger/logspout:master
Untagged: quay.io/subledger/logspout:master

$ docker pull quay.io/subledger/logspout:master
Pulling repository quay.io/subledger/logspout
40a52d6ca462: Download complete 
511136ea3c5a: Download complete 
0114fb636191: Download complete 
da123f3e1538: Download complete 
5e40189e370a: Download complete 
cda1eb1e2e14: Download complete 
5abbcbd32e90: Download complete 
6f4245c735ea: Download complete 
5d6de418c9de: Download complete 
Status: Downloaded newer image for quay.io/subledger/logspout:master
quay.io/subledger/logspout: this image was pulled from a legacy registry.  Important: This registry version will not be supported in future versions of docker.

$ docker history quay.io/subledger/logspout:master
IMAGE               CREATED             CREATED BY                                      SIZE                COMMENT
40a52d6ca462        9 weeks ago         /bin/sh -c #(nop) ONBUILD RUN cd /src && ./bu   0 B                 
5d6de418c9de        9 weeks ago         /bin/sh -c #(nop) ONBUILD COPY ./modules.go /   0 B                 
6f4245c735ea        9 weeks ago         /bin/sh -c cd /src && ./build.sh "$(cat VERSI   9.621 MB            
5abbcbd32e90        9 weeks ago         /bin/sh -c #(nop) COPY dir:b7de7efabd9eb9bba3   90.86 kB            
cda1eb1e2e14        9 weeks ago         /bin/sh -c #(nop) EXPOSE 8000/tcp               0 B                 
5e40189e370a        9 weeks ago         /bin/sh -c #(nop) VOLUME [/mnt/routes]          0 B                 
da123f3e1538        9 weeks ago         /bin/sh -c #(nop) ENTRYPOINT &{["/bin/logspou   0 B                 
0114fb636191        5 months ago        /bin/sh -c #(nop) ADD file:ab9e2f3982a65d1cf4   5.041 MB            
511136ea3c5a        2 years ago                                                         0 B                 Imported from -

How did the image ID change from 5e0980f79b63 -> 40a52d6ca462?

Did you find the reason or root cause?