Unable to Add a New Expense

When I try to add an expense, it pre-fills the form with the values of my last one. The problem is, the last expense I added was in an earlier VAT period so it's now locked - the new expense automagically has the same date as the last one so it's also locked and I can't change the date to unlock it.

I know I can get around this by temporarily unlocking the last VAT period but is there a more elegant solution?

Cheers
Simon