Crash when deleting entities from a deserialized world (entity not found)

I've been using Legion in my Nox Futura Rust port. It's generally excellent, but I've run into a bug. I didn't think you'd want to help me go through 13k lines of code, so I made a repo with a reproduction of the issue: https://github.com/thebracket/legion-serialize-bug-demo

It uses the serialization code from the example, wrapped in some functions. This is working _great_ with 30k entities in NF, loading nice and fast and all the queries/systems work with the loaded data. I know that Entity references in serialized data aren't done yet, so I've been using an identity tag (with a unique id) on entities I need to reference - with a view to replacing it with entity references at a later date. That's also been working well.

The bug: when you try to delete a deserialized entity, you get a crash. Legion appears to be unable to find the entity (even though it hands it to you and it looks ok, and referencing its components works fine) and crashes on an `unwrap` call. I've included full backtraces and example usage in the linked repo.

The example:

In `works_fine`:

1. Inserts 3 trees into the world. They have `TreeTag`, `IdentityTag(usize)` tags (the identity is incremented per tree) and a `Position` component.
2. It runs a query to filter to tree id # 1 and prints it.
3. Runs a query with entities to find tree # 1 and deletes it via a command buffer.
4. Searches for tree # 1 again to show that its actually gone.

That works great.

In `crashes()`:

1. Inserts 3 trees into the world. They have `TreeTag`, `IdentityTag(usize)` tags (the identity is incremented per tree) and a `Position` component.
2. It runs a query to filter to tree id # 1 and prints it.
3. Saves the world to a RON file, and re-loads it.
4. Finds tree # 1 and prints it again to prove that its there.
5. Runs a query with entities to find tree # 1 and deletes it via a command buffer.
6. It crashed!

Hopefully, I've just done something wrong in my copy/paste serialization code?

Thanks for taking the time to look at it. Legion is awesome.