Scenario
1. You create a backup plan with a pre-set template for schedule - "Weekly full, Daily incremental"
2. You expect to have only the set amount of full backups, but in fact each month one extra is generated on the first day of the month.
Cause
There is an issue in the product that causes creation of a FULL backup, if the backup plan is run for the first time in the month.
Solution
The issue will be fixed in future updates of the product.
As workaround, create backup plan with a custom backup scheme.