Calls into object subclasses that are still floating can cause reference issues

[sdroege]

For virtual methods we ensure that the object is still floating once the virtual method returns and not floating during the scope of the virtual method. However the same problem would happen if other callbacks with the floating object would happen, any kind of callback. The first use in the bindings in a transfer none context would sink the floating reference and cause memory leaks or worse.

Unclear how to handle this other than using the floating reference guard in all callbacks, signal handler trampolines, etc.

[sdroege]

As this now actually causes crashes in practice and I have a plan that improves the situation at least, let's block the release on this too.