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I was able to see this problem in your jotform http://www.jotform.ca/form/51755082536256
the issue is being caused by erroneous condition rules that updates the Price textbox.
I suggest you re-design the form and use Calculation Value instead.
user guide: -How-to-Assign-Calculation-Value
and remove the condition rules that update the Price
You can check my test form http://www.jotformpro.com/form/51761003398959
You can clone the test form also. -How-to-Clone-an-Existing-Form-from-a-URL so that you can check in your Form Builder how I setup the form.
Let us know if you need further assistance.