Were these DPNs (double pointed needles) or circulars (two needles joined with a cord)?
I'm wondering: If they're circulars, were you straining to make the tips meet and maneuver correctly to knit (sometimes this will happen if your cord is really short)? If so, that might put too much tension on the needle part and make them bend. You might try longer cords and magic loop
or traveling loop
, or you could try DPNs instead.