Yes, it is a bug. I haven’t been able to figure out exactly what steps causes it to occur, but I have experienced it on multiple occasions with various versions of Carbide Create. For every time except for the latest event, I had been lucky enough to catch it before using the gcode. I have never set the retract height to zero, but somehow it is set to zero once in a blue moon on me.
A fix on an intermittent bug will not be forthcoming any time soon unless someone figures out the exact steps to cause it to happen. In the meantime, a warning should be given when either saving gcode or sending it to Carbide Motion that the current retract height is set to zero.