I have created a very simple repro of this issue with a small checking account with a few transactions:
Then in budgets I create a simple budget with 10 per month for tolls and 100 per month for everything else in the auto category. I have the same budget every month and rollover enabled.
The expected result is that the balance for February is $-395 =(110 - 510 + 110 - 105) however an incorrect balance is shown of $-795.
If I add a specific line item for service and parts so no transactions land in everything else the values are correct
Note this is with a brand new file with no chance of being corrupted.