Hi Julie,
I did a similar case in my test system, it is showing similar. Tolerance had no impact on the plan date with your scenario.
Last call completed is on 07/07/2014
For call 3 Next call planned is on 07/07/2015
For call 4 Next call planned is on 07/06/2016
To know why it took on 6th July 2016, the reason is because of Leap year.
Why the date is different, is because you have chosen TIME in scheduling parameter, if you choose TIME- KEY DATE, system will work as per your requirement, there will not be any difference in date.
Regards
Terence