Material ID (Cycle) on Birth Spline

[WillW]

I'm not understanding why I can't get my birth spline ID's to cycle like a normal birth operator does. The only difference between these two events is the method of birth and you'll see that with the regular birth operator, my matID's are cycling correctly, whereas with the spline, the matID is stuck at 1.

Is this a bug or am I missing something?