Questo funziona anche con il DIV in larghezza a percentuale:

<div style="width: 30%; border: 1px solid red; overflow: auto;">
gggggggggggggggggggggggggggggggggggggggggggggggggg ggggggggggggggggggggggggg


gggggggggggggggggggggggggggggggggggggggggggggggggg ggggggggggggggggggggggggg


</div>
prova a processarlo da solo, può darsi che il problema derivi da altri contenitori superiori.