I realize this thread is 3 years old, but I was having this same problem this week and was finally able to figure it out. Adding my experience with this problem here in case someone else has the same problem and comes across your post in the future.
Issue: When reclassifying data in ModelBuilder, I was not able to edit the final value in the "new" column from "NoData" to "10". It would revert back to the previous value as soon as I clicked out of the value box or ran the tool, the same as the original post.
Solution: press enter after inputting the final "new" value. That's it. Clicking out of the value table caused the final value to revert every time, but not if you press enter. The previous values were saved because I was clicking out of their new value boxes into the next new value box, but since I would just click somewhere outside of the table after entering the final new value, it wasn't saving it.
