We're on 5.0.16 and it continues to be an issue with child accounts, but if you instead share out the root of the child account and have the parent set up a persona for the from address, that probably works more like you're looking for.
zmmailbox -z -m <child@domain> mfg / account <parent@domain> rwidx (give parent manager permissions to root of child account)
zmmailbox -z -m <parent@domain> cm /<desired folder name on parent's view> <child@domain> / (add child's root to parent's folder view)