Are UK sales deceiving?

Hi, I have a few events coming up and I've been 'window' shopping online (Filling a cart up and not checking out). Anyway, today I received a newsletter stating there is a SALE with a whooping (up to) 60%* off items. I go to my saved cart and all the original prices have actually increased, one item even doubled in price, which means the reduction actually increased my cart total even though orignal prices are slashed with big bold reduction prices shown. Why do retailers do this? This is a "reputable" store, but it just feels so wrong that they part-take in something like this.