[vanilla] workers prompt bug in vanilla Civ5

[Naokaukodem]

When a military enemy unit comes close from one of my workers, this last won't achieve its task without prompting me every turn, that long after the menace is out (50 turns ?). This is true especially in conquered lands, and is so unpleasant to me that I uninstalled the game. Can this be fixed with a mod ? Thank you very much.