Unless you adjust the savings amount manually, it just assumes that you put $75 “in the envelope” every month since you started budgeting for it and never took any money out (e.g. your actuals for that category are $0).
You can adjust the savings amount for the lawn category to reflect the actuals savings that’s really in the envelope if you want or just modify the budgets on the Categories sheet so that any prior months have $0 for the lawn budget and just enter it in the month where it should start accruing so it’s not accruing falsely.