Advancement "parent": "<namespace>:<file>" x4+

For some reason, if I parent an advancement that's already 3rd in the chain, it and any following vanish. Why is this?
Tree:
mppr
|-welcome
|-basics
 |-stageone
  |-stagetwo
   |-stagethree
    |-stagefour
|-advanced

Stage Three and Four don't show unless I parent Three to Basics. I want each set to be it's own line, not split multiple lines.