Deadlock in OpenJFX 9 at Platform.exit()

We noticed that after a Windows PC (running JDK 9 EA) resumed from about sixteen hours of hibernation, a previously well-running JavaFX application lost sime kind of its previous agility wrt to rendering (i. e. it got "viscous" while it was "fluent" before). So we tried to stop the process by invoking "Platfrom.exit()" which we expected to simply "tear down" the whole thing unconditionally.

To our surprise, what we got was a deadlock. This means, "Platform.exit()" apparently is conditional to some extend.

We like to kindly as for (a) investigation of the attached stack trace to tell use whether this was "our fault" or "your fault", (b) to decide whether it is actually intended that "Platform.exit()" might get deadlocked at all.