After upgrading to Java 8 update 311,
java.lang.ClassCastException: ....swing.FCheckBox$FCheckBoxModel cannot be cast to javax.swing.JToggleButton$ToggleButtonModel
Exception thrown.

java.lang.ClassCastException: com.xxxxxxx.swing.FCheckBox$FCheckBoxModel
cannot be cast to javax.swing.JToggleButton$ToggleButtonModel
        at javax.swing.LayoutFocusTraversalPolicy.accept(…)
        at javax.swing.SortingFocusTraversalPolicy.getComponentAfter(…)
        at javax.swing.LayoutFocusTraversalPolicy.getComponentAfter(…)
        at java.awt.Component.getNextFocusCandidate(…)
        at java.awt.Component.transferFocus(…)
        at java.awt.Component.nextFocus(…)
        at java.awt.Component.transferFocus(…)
        at java.awt.DefaultKeyboardFocusManager.focusNextComponent(Unknown Source)
        at java.awt.DefaultKeyboardFocusManager.processKeyEvent(Unknown Source)
        at java.awt.Component.dispatchEventImpl(Unknown Source)
        at java.awt.Container.dispatchEventImpl(Unknown Source)
        at java.awt.Component.dispatchEvent(Unknown Source)
        at java.awt.KeyboardFocusManager.redispatchEvent(Unknown Source)
        at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(Unknown Source)
        at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(Unknown Source)
        at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(Unknown Source)
        at java.awt.DefaultKeyboardFocusManager.dispatchEvent(Unknown Source)

No issues with 8u301.