Quality bars are meant to have a flex point in them. That's called a live bar and will have a better torque to it. High grade steel Olympic bars, for example, require that extra spring. They are designed for heavy weight on them. Exercises bars, usually cold pressed steel, are more stiff (also reffed to as dead) and may tend to bend and get out of shape more quickly. The cheap "Olympic" bars from China and India (usually around $100...with plates) are poor quality material and will tend to bend or even snap under heavy loads. You can use much more weight on a exercise with a live bar as opposed to a dead exercise bar. I have used a Swedish and Russia Olympic bar, preferring the Swedish one a little better. Though most of the bars at our club are York.
I find that the best squating is with a old used bent bar, at the center (you can buy squating bars with a slight bend in the center). Seems to fit the shoulders and traps very well, as if by design. We have a couple of 9ft Olympic style bars for power rack training. Do not know who made them, but excellent spring to them for handling extra heavy weight when doing squats and DL's.
If TWT's bar was bending that much that it looks like an upside down letter "U" than it is of poor quality. With 550 there will be a normal spring and bend, that is to be expected. But not to that extreme. May want to avoid that bar in the future, can throw your balance off and affect the knees/lower back, etc. with an injury. Might try just rolling the bar off the shoulders or jump straight ahead (very quickly) to clear the falling bar/weight.. Good Luck.