Hi @Jason_Cohen and thanks for reaching out in the Forum!
This could well be a bug, but in order to investigate, we would need to take a look at these tasks in our system, so I think our support team will be in a better place to assist you. Could you please reach out to them following these steps: https://forum.asana.com/t/how-do-i-contact-support/19057/7?u=marie and provide them with the info below:
Email address of your colleague with Comment-Only access to the Project
URL of the initial task
URL of the new task after completing the initial one?
With this info our team will be able to launch investigations! Again, so sorry for the trouble @Jason_Cohen; let me know if there is anything I can help you with!