Success! Here was the problem:
In the init of my parent bizobj (calinfo) on page one I had the following code:

this.AddProperty("ocalday")
this.ocalday = createobject("calday")
this.registerchildbizobj(this.ocalday)

Then I was setting my cparentibizobj in calday (the child) to calinfo. After commenting out the three lines of code above, the form started closing. What I am assuming is that MM controlled the parent/child relation automatically when I used the builder, and that the above code was making a second reference to that object.
It hadn't even occured to me that that was it, because I assumed it had to be there.
Thanks for all your help!