JavaFX build: 8u40 b12
Steps to reproduce:
1. Start VoiceOver on Mac OS X 10.9.5 and 10.10
2. Run HelloCheckBox
3. Press Control+Option+Space, when the state is indeterminate, on 10.9.5, VoiceOver reads "check", but on 10.10, it reads "uncheck". Neither of them reads "mixed".

It works with VoiceOver when pressing only "SpaceBar" to change the state. VoiceOver reads "mixed" for indeterminate state.
On Window 8.1, when pressing CapsLock+Space to changes state to indeterminate, Narrator reads "indeterminate".