At the moment, Case Management supports only the use case of having one case owner which is assigned to the case when starting a new case instance.
Case Management Showcase App exposes case owner assignment via required Case Owner input field placed in the dialog which is used to start a new case instance.
This input field has set as a default value the user who is currently logged into Case Management Showcase App.
However, the input field allows replacing the default value with just a space, with a comma separated list of entries or with a single entry preceded/followed by arbitrary number of spaces and commas. This in turn creates an invalid case owner assignment when starting a case instance.
The case owner assignment can't be changed during the case instance life which leaves running case instance in a broken state if the case contains user tasks assigned to owner role at case design time.