I do not have that version, mine is a B+W 82mm UV Haze Slim MRC 010M Filter.
I am not sure XS-Pro version was available yet when I bought mine. It has been a few years.
I am sure some have had filters for years that they swapped over to the new lens.
Roger didn't name names or brands, I wish he had named brands and models.
This was Roger's final word on it and the word "and" was not used.
"My suggestion, though, is that you stay away from ultra-thin filters on these lenses, especially discount ultra-thin filters. If you look across the front of your lens from the side, you can get an idea how far up the center of the lens bulges. Then look at the back side of your filter and see how far the glass is from the bottom of the threads. If those two distances seem similar – well, be careful!"
Bringing this back around to the OP.
It looks like all of the retailers have raised the price back up as of yesterday, maybe even Thursday. Given that this wasn't a prolonged price drop, either they cleared the inventory they wanted very quickly or there was a glitch in the pricing at Amazon and B&H/Adorama followed. Given that the price reduction was $300, the same as the current mail-in rebate, I am thinking someone mistakenly applied the mail-in rebate as if it were an instant rebate.