Why does the constrained object “flip”?

It’s caused by the Z-up problem. This means that when using a constraint that does not specify the way the Z-axis of the pivot faces (for example, look at constraint, path constraint), Bongo assumes that you want the z-axis to face towards “up” (ie - world +Z). This keeps the object stable in what would otherwise be a non-fully constrained system. However, it does mean that when the object pivot z-axis is forced to point downwards by the constraint, you may find that at that point the object will “flip” as it attempts to keep the z-axis pointing up.