UserAgent: Mozilla/5.0 (X11; CrOS x86_64 8350.31.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.41 Safari/537.36
Platform: Multiple

Steps to reproduce the problem:
1. Position the shelf on left or right
2. Use Chromebook normally for an indeterminate period of time, doing currently indeterminate things
3. The shelf shifts from the side to the bottom and cannot be repositioned on the side again without first restarting.

What is the expected behavior?
Shelf stays where the user positions it.

What went wrong?
Unknown cause, but possibly related to tab interactions. There are a couple reports that the bug occurred shortly either simultaneous with or shortly after closing a browser tab, but this is not confirmed.

Did this work before? Yes Previous stable version of Chrome OS

Chrome version: 51.0.2704.79  Channel: stable
OS Version: 8172.47.0/1/2
Flash Version: 

The following Chromebook Central Forum threads all have to do with this issue. I have also experienced this issue. Unfortunately we have been unable to identify reproducible steps

https://productforums.google.com/forum/#!topic/chromebook-central/aiPqP0_t7wA;context-place=forum/chromebook-central

https://productforums.google.com/forum/#!topic/chromebook-central/V0HliNTAh5E;context-place=forum/chromebook-central

https://productforums.google.com/forum/#!topic/chromebook-central/StMJ32yT7u8;context-place=forum/chromebook-central

https://productforums.google.com/forum/#!topic/chromebook-central/OIdyLPtPPNs;context-place=forum/chromebook-central