Get assertion failed

I happened to run into this error running [`papaya`](https://github.com/ibraheemdev/papaya) under bustle.

```
thread '' panicked at 'assertion failed: `(left == right)`
left: `false`,
right: `true`: get(17225765586053087836) 19337850 145067 12727980', /home/ibraheem/.cargo/registry/src/index.crates.io-6f17d22bba15001f/bustle-0.5.1/src/lib.rs:464:21
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
```

I cannot reproduce it and I have no idea how it occur because it seems to indicate that `get` returned a value even though `remove` succeeded on the same thread. I'm not completely familiar with how bustle chooses operations, is it possible that I ran into a rare bug where `bustle` allowed another thread to insert the same key again?

The workload did not include any updates or upserts, if that simplifies things.

Start by examining the assertion at bustle-0.5.1/src/lib.rs:464 and the workload behavior described when running papaya under bustle. Investigate how bustle chooses operations and whether another thread can insert the same key after removal. Done means identifying a reproducible cause or ruling out the suspected scheduling issue.

Written by the indexing model from the issue text.