Time bars not always visible.

Sometimes the time bars do not display in the Timeline Palette. In image below with everything except Cylinder expanded in the layers named Left and Right the time bars for layer Left do not display.

Now I expand Cylinder and everything looks fine.

Same if I collapse  Cylinder2.

I am not sure exactly how to re-create this bug as it seems pretty random but it is related to what is expanded and what is collapsed in the Timeline Palette.