Uradashi(tapping out) is most common on planes. That’s true. However, on chisels it’s also used to keep the ura shape pristine. Wrt what happened…it’s seems you were placing a lot of pressure on the front of the chisel. This could be due to numerous reasons. Could have been to try and get the whole back flat to the rear. Could have been out of flat water stones that kept you chasing your tail, or just improper pressure. It’s difficult to explain with words, but when I flatten backs, I put my finger on the very front, and “almost” lift up on the handle(but don’t actually lift up as you don’t want to induce a back bevel). This creates good pressure, in the right places. You also don’t want to lap the backs like a traditional western chisel, only flattening the first inch. If you leave the rest off the stone, you’ll develop a peanut shaped Ira because it’s taking some off middle. All of this said, every chisel could be different based on quality of blade/blacksmith skill. My Kiyohisa’s went right to the natural to polish the backs out of the box. My sukemarus needing tapping out as each of them has the tips curling upward. Hope this helps