This happens when you have more than one conversion goal turned on. With forms you can track leads as conversions, while links on images/buttons/text only track clicks as conversions. If you have both enabled, then in the analytics reporting you will see the total number of conversions generated by all the forms and all the links that you are tracking.
If you wish to only track new leads as a successful conversion then make sure that you have a form element on your page and that you only have form submissions selected for conversion tracking.
If you are tracking both, then the difference between the number of conversions and the number of leads is represented by the number of link clicks.