In 8.2.x, when a field is disabled under "Manage display" for an entity, the label display settings still appear to be configurable. However, the user's selection is not actually stored anywhere and therefore lost.
(gif provided by @alexpott)
In 8.3.x following
This bug might not appear that impactful at first since it's for configuring fields that are not displayed, but the problem is that this also impacts the data when fields are moved between disabled and an enabled region, which results in lost input that the user did not expect.
Steps to reproduce
/admin/structure/types/manage/article/display, move the Tags field to disabled and save the form.
- Change the "Label" or "Format" options for the Tags field and save again. The change is not actually saved.
Do not show field settings that are not saved for disabled fields.
The solution will need to support all three of tabledrag, non-tabledrag, and no-js workflows for the form.
A different solution would be to actually store the configured settings for disabled fields, but that would require a data model change as well, and as @alexpott points out there is also an advantage to simply having fewer options on this form.
User interface changes
Data model changes