If you have 0 cash, it resets the price to 0. If you have a very small amount of cash (say, 500) it'll set the per-point price to that amount ($500 in my example.) If you have enough cash that the point price is lower than your cash on hand, then it doesn't give a damn what price you put in per point, it picks it's own default amount and makes you use that amount.
So for practical purposes, you can't sell points unless you want to keep cash on hand and let the system choose a price for you.
I tested with Firefox (my usual browser) and with Chrome, same results.
Please add to that report if you're still having issues along with more details (such as what number it's going to, is this number the cash amount you have on hand, etc)