This has been going on from 0.13.0 to 0.15.7. If you press the E button while renaming an item in an anvil, it closes out of the anvil inventory. This only works/happens on Windows 10.
MCPE-17014
Pressing E in Anvil menu (Windows 10 only)
Resolved
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@unknown, How many times have you been asked to search for existing tickets before creating one?