Crash attempting to downgrade to 1.7.10

Put the summary of the bug you're having here

What I expected to happen was downgrade to 1.7.10 from 1.8 so I could attempt to fix an anvil bug on a 1.7 server.
Describe what you thought should happen here the anvil should work correctly

What actually happened was stole my lvls and materials.
Describe what happened here

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
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