We've made transaction splitting available in Money Management Tools. This is useful when you go to a store where you can buy anything from groceries to automotive supplies. In the past, you were required to pick one category for the entire transaction which didn't represent how you actually spent your money. Now you can break the transaction into separate ones, each for its own amount, and assign separate categories.
To undo a split, click on one of the split items to edit its details. You'll see the Split This Item button has changed to This is a Split Item. Clicking that button will bring you back to the splitting screen. Just click the X next to the rows you want to delete. The amount is added back into the last category listed.
One thing to note, you should split your transactions prior to applying any notes or labels. Once the item is split, the new items act as separate transactions so you can apply separate notes or labels to them in addition to separate categories.