A chain of if/else if statements is evaluated from top to bottom. At most, only one branch of the chain will be executed: the first one with a condition that evaluates to true.
Therefore, duplicating a condition in a sequence of if/else if statements automatically leads to dead code. Usually, is due to a copy/paste error. Obviously it could lead to unexpected behavior.
if (param == 1) openWindow(); else if (param == 2) closeWindow(); else if (param == 1) // For sure this is a bug moveWindowToTheBackground();
if (param == 1) openWindow(); else if (param == 2) closeWindow(); else if (param == 3) moveWindowToTheBackground();