From today I've seen that error message.
If I try to create task from anywhere - Project page, Project work board, My favorite menu, shortcuts or any I receive stopping message as:
> Edit Locked Task
> This task is locked. Edit it anyway?
Have a answer that it's coming from new feature T12335
The revision of local install is:
> commit 9124bb416241bb117d50ced260e3b23e830882dd
> Merge: 216f6be 8e26916
> Author: epriestley <git@epriestley.com>
> Date: Sat Mar 4 16:18:38 2017 -0800
>
> (stable) Promote 2017 Week 9