With the Wunderlist integration, any tasks that are submitted are done so based on the user that initially set up the configuration. In other words, regardless of who submits a task, only the user listed in the Logged into Wunderlist as... section of the integration configuration will be used.

A helpful feature would be support for multiple Users on a given task list. Wunderlist allows for multiple contributors on a list, so a way to dictate which account is the submitter based on a /command or automatically from the HipChat account adding the task would allow for more flexibility and ownership.