If you start to hold your spacebar, and then when you open any inventory (chest, etc.) you will continue to jump while in the inventory even if you let go of the spacebar. As soon as you exit the inventory, you will stop jumping.
This bug shouldn't generally affect people during gameplay in a negative way, but it is important to squash those bugs!
Thank you for your report!
We're already tracking this issue at MCPE-54571, so I will resolve and link this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated. If you haven't already, you might like to make use of the search feature to see if the issue has already been mentioned.
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