CAUSE @ EFFECT
When you place a Shulker box on the same block you are on it teleports you 1 block up next to the box.
NOTES
I Highly recommend trying this yourself and seeing it for yourself.
Might not be a glitch.
The same behavior does not happen with chests.
Related issues
Comments
[Mod] Celesian
migrated
Thank you for your report!
However, this issue has been closed as a Duplicate of MCPE-39674.
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