The modal for custom task types has been recently redesigned since its initial launch. Although it may appear to have a clearer UI by separating/grouping the incomplete / complete statuses, it has broken the possibility to mix a complete status within the list of incomplete statuses; something that the previous modal allowed for. 
With the new modal, we are now forced to group all the Complete statuses at the bottom of the dropdown list, which I believe is a serious short-coming of the new modal design and I would suggest this ability is reinstated as it has broken several workflows for my customers.
In certain use cases, the completion status could come prematurely and not necessarily at the end of the workflow. The issue is that the dropdown list of statuses of a custom task type reflects the sequence of a workflow and helps the users move the task onto the next status or step of a workflow. If the completed status are all at the bottom, this breaks that user experience, that was previously available.
Before
Note the position of ‘Budget rejected’ which is right after ‘Budget approved’
(ignore the scribbles, it’s from an older screenshot that was marked up for another post)
Note the sequence of statuses within the dropdown followed a specific workflow. Budget rejected was an option positioned right after Budget approved:
Now (broken)
Note that the position of ‘Budget rejected’ has now been forced to move down, below ‘In development’
The sequence of statuses does NOT follow the specific sequence of the workflow.
‘Budget rejected’ has now been forced to move down, below ‘In development’
Kindly consider reinstating the ability of mixing completed statuses within incomplete statuses for custom task types. Thanks!