Adding 1 to a variable adds 2 instead. If I add 0 to a variable it adds 1.

I have created a custom quiz, it all worked perfectly for my first course but when I have saved a new copy and edited the quiz answers for a 2nd course, some questions now add 2 to the quiz total instead of 1. The triggers are identical, all I have changed is the text attached to each radial button. 

If I program the Submit button trigger to add value '0' to QuizTotal, it adds value '1'
If I program the Submit button trigger to add value '1' to QuizTotal it adds value '2'

I have deleted the triggers and manually re-entered them but it still adds the wrong value. 

My quiz works with 2 triggers on the submit button. The first says if radial button 1 = selected and radial button 2 =not selected, add value 1 to QuizResultQuestion1

Then there is a second trigger to say if QuizResultQuestion1 = 1, add value 1 to QuizTotal. 

I have even added a trigger to say set QuizResultQuestion1 to value 0 when the slide loads but this didn't make a difference. 

If I set my first variable, QuizResultQuestion1 to a value of 2 instead of 1 and then add 1 point to the QuizTotal if the QuizResultQuestion1 variable has a value of 2, it fixes the problem.... but creates another because I don't want QuizResultQuestion1 to have a value of 2. 

Some questions work perfectly, some have started adding an extra point. 
Has anyone experienced this issue?