Stage.show() blocked for several minutes

This is a follow-up to JDK-8088707.

Sporadically Stage.show() is blocked for several minutes! The problem only occurs if the computer resumes from hibernation, and the actual duration of Stage.show() varies from seconds to many minutes. Example: Computer was in hibernation for few hours, then Stage.show() needed about four minutes (!) to present the window.

Using jvisualvm I drilled down the "freeze" (please find attached files) and noticed that the causer in fact is ListChangeBuilder.insertRemoved(), which is invoked deeply within Scene.clearNodeMnemonics(). According to jvisualvm insertRemoved() consumed more than 240.000 Milliseconds! The application, BTW, has no menu at all; the sole mnemonic used is found a Button.

Attached you will find:
* A JVisualVM profiler snapshot showing that 222.000ms have been spent inside insertRemoved().
* Two threaddumps taken while Stage.show() was "frozen", in several minutes space. They are showing that the profiler really seems to be right, as both threaddumps show that the FX Application Thread is (still) working on insertRemoved().

This is pretty ugly, as apparently there is nothing the application vendor can do to work around this effect. So if there is something you like me to try, please don't hesitate to tell me. :-)