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 checked again, it will still be unchecked. However, it should become checked again, if it was checked before.
It sends a misleading message that that option will be applied, e.g. that autoblocks would be applied for this block (and you can't prevent that from happening):