When my brother in law is benching 450+ a 45lb bar bends too... not too worried about it breaking though.
Typically I would think that if it came as a set... then that set can handle all the weight it came with. IE if it came with a bench, barbell, and 300lbs of weights, I'd imagine the bar can handle the 300lbs, flex or no flex.
If you're that worried about it, just get a larger bar.