Bone tool (Inverse Kinematics) tool icon disappeared?

Has anyone else mysteriously lost any toolbar icons?

My IK / Bone tool icon is gone. I can still access the editing mode with Shift+I, but I cannot get the icon back in the toolbar with the rest of the tools.

I have been working in Harmony for months now and this has never happened. Restoring the default workspace didn’t bring it back. I can’t customize the toolbar to add the tool. If I am</em able to customize any toolbar, the IK tool isn’t an option.

It’s not a deal breaker, since I can still access the mode with the keystroke, but it’s unsettling that I can open the app one day and the UI is changed for no apparent reason.