You may have formulas in your source budget that also need to be copied.
When you build formulas in Budgyt, they live in the budget in which you created them.
This means that when you copy data from one budget to another, you might copy across the inputs to the formulas, but the results won't populate unless you also copy the formulas.
To do this, go to Data/Formulas > Copy Data, and choose Copy Formulas from the drop down menu at the top left of the form, and copy your formulas to your target budget. Now these formulas will operate on your copied data and your numbers should be correct.
When copying formulas, only the formulas that you copy will appear in the target budget. They will not be added to any formulas that are already there, these will be deleted.