IIRC from the old forum, being unable to delete the last digit in the split items pane was a result of changing something else. You can use the balance symbol to even out the gold, or type the full number in and then delete the left-over digit from the original value.
Some people have found that repairing items in their inventory or on the ground is more reliable. I ran into this, but mostly in one possibly corrupt quick-save, and got into the habit of saving before repairing anything.