for example, if you turn on the 3 checkbox difficulty options in this order left to right in one go: Friendly, Enemy, Mines on Extended Map Content, then the last setting (Mines) will be switched off

if you only turned on one difficulty setting, then it's reverted right after you apply it and the game options menu closes, so it always reverts the *last* checkbox difficulty setting you have customized to what it was before

note that this doesnt happen to the drop-down menu or the slide options (AI Skill, AI Precision) and only happens to the checkbox settings like Vision Aid