My gut feel is that the vehicle market is taking a hammering on the back of either a slowing economy or an anti diesel drive by government and councils or both.
If the return vehicle isn't worth its predicted value, then they are going to find some way of recouping losses.
Its a repeat of what happened in 1999 when the 'Rip off Britian' campaign got into full swing and knocked thousands off the price of new vehicles. (A Citroen Xsara LX became a Forte with a £2000 price reduction. The mechanics had to go around each stock LX vehicle and change badges from LX to Forte. Any vehicle purchased by the finance houses before that lost a slice of value in the blink of an eye. It was the finances houses that lost out and boy, did they try every tactic in the book to make the customer pay on return vehicles.)
I'm not against leasing, but you need to be in control at the end of the lease. Try to get that balloon payment smaller by increasing your monthly rental and go for a personal lease purchase (PLP) that will allow you the own the vehicle once the final payment and transfer fee are paid.
Leasing is all about the new vehicle price, depreciation and the profit for the dealer/finance house. How do they know how much a new Ford Courier is going to be valued at in 3 or 4 years time with 60,000 miles on the clock? They don't. They can only take an 'educated' guess on what the trend has been over the last couple of years and apply that. Its a gamble and when the finance house wins (the return vehicle is worth more than they projected) they are happy, but when its lower they aren't.