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I took a look at the Form Designer and did not have any issues with it. I even cloned your jotform to make sure that the issue is not with the jotform itself, but I was able to save the changes as well.
Would you please mind using FireFox to see if it works for you?
If it does the issue would be caused by your browser cache and could be resolved by following the next steps: 15 Ways to Clear Your Browser's Cache - wikiHow
Do let us know if you continue experiencing the same issue with FireFox as well.