Logging into a changeset that belongs to a task is not done automatically when it is selected in South panel. The red color indicates that you are not logged in to the changeset that is connected to the task.

To log into the changeset that is connected to a task, press Log in into changeset. The row then appears as blue.

If the current user is not the owner of the task and the changeset, the login will result in a read-only mode.