Widgets on the Special:Block page should remember their default checked state, or if the user has interacted with them, the state that the user set.
Since T212391, checkboxes are enabled/disabled depending on the block parameters entered in the form (previously they were hidden/shown).
If a checkbox is disabled, it is also unchecked, to indicate that the option cannot be chosen for the particular block parameters entered. If the parameters change and it becomes enabled again, it will still be unchecked. However, it should become checked again, if it was checked before.
Note that the checkbox should not just remain checked in the disabled state, since it sends a misleading message that that option will be applied. E.g. it looks as if autoblocks would be applied for this block (and that the admin can't prevent that from happening), but in fact autoblocks would not be applied: