Drop of COM class not working in webview2 example?

[AndyT-MS]

I'm getting a panic when running examples/webview2.rs because environment still has a strong ref count of 2 at the point of calling try_unwrap on it, despite the explicit call to drop(handler_class) earlier. The first line in the below output is a debug println! that I added to display Arc::strong_count(&environment) and Arc::weak_count(&environment) just before the try_unwrap call and after the drop(handler_class) call.

Strong: 2  Weak: 0
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Mutex { data: None }'

Although I'm generally calling the real WebView2Loader.dll in my code, the error repros without it. I still get it when I comment out the whole call to CreateCoreWebView2Environment on line 77, and that's why data == None in the above output rather than an actual object.

Is this a bug in the generated Drop implementation for CreateCoreWebView2EnvironmentCompletedHandler? It's also possible that I'm just missing something that should be reasonably obvious because I'm still very new to Rust.