I don't get this. I got the car from 4k miles. At 7k miles i asked for an oil change as the oil haven't been changed for a year. Fair enough. They did the oil change and the new scheduled oil change on the idrive jumped to 12K. I didn't noticed it at first.

So i arrange for the 12K change (and by the way, the schedule changed by itself to 11K on the idrive menu a week before i go to the dealership!) and that was done on Thursday. Guess what, new oil change now due on 16K.

What is going on here ? Is the dealer fiddling around with the I-drive inputing short oil change intervals ? Fair enough i would have done these by myself as i always change the oil between 5-7k but ... isn't supposedly BMW oil intervals long ?

The system is telling you the number of miles 'till your next change' not 'what the odomerter should read'. I believe the system takes several measurement, but generally set the interval at 14-15k after each oil change. It will count down the miles till your next. You don't need another oil change till it hits '0'.

I totally agree with ceenit. The iDrive is telling you the miles LEFT before you need a change. The dealer I go to will not do an oil change until the iDrive reads close to 0. I got my car with 13000km (8000mi) with no oil change service ever recorded. The iDrive said 19000km (12000mi).
Current mileage is 17500km (11000mi) with 17000km (10500mi) showing on the iDrive. It all depends on your driving style, speed, etc to determine the state of the oil.
My retired 2003 325iT was always reset to 25000km (15500mi) after a change.
I would say you have had an unnecessary change and can wait until 16000mi before the next one. The iDrive should slowly count down. There is a 'time' component built into the system but I am unfamiliar with it. My 2002 Mercedes resets to 15000km (10000mi) or 13 months.

I wouldn't wait 15K miles for an oil change (if you plan on keeping the car). I'd spring the $100 for an in-between oil change after 7.5K miles.

This oil change argument pops up on every forum. These cars are designed with longevity in mind and the use of synthetic oil which is significantly superior to the old 'dino' juice of the old days. Over the years the length of time between changes has gotten progressively longer. Car companies spent exhorbitant amounts of research dollars on their engines.
Twenty years ago, I would agree with you. Today, IMO, you're wasting your money. Since my first Mercedes in 1979 and subsequent Mercedes in between up until now (second BMW), I have never had extra oil changes beyond the manufacturers suggestion. And I have never had any engine issues. I buy my cars outright and usually keep them 5 years.
Most car owners who grew up driving the former 'Big Three' cars seem to adhere more to the 5-7000 mile oil change mantra. European cars have always had longer oil change intervals. I don't know why. Maybe better engines?
Hey, everybody has a strong opinion on this subject. Peace.