Version: 53.0.2785.116 (Official Build) (64-bit)
OS: Linux

What steps will reproduce the problem?
(1) Enable --experimental-web-platform-features
(2) Visit http://jsbin.com/megowi/edit?html,css,output
(3) Scroll down.

What is the expected output?
Sticky box should move down when it begins to stick and stop at the bounds of its container (i.e. it should look identical to the container on the left but scaled up).

What do you see instead?
Sticky box does move down when it begins to stick but moves farther than its container's bounds.

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