Highlights - Hungarian Grand Prix
By Mark Hughes
BBC F1 commentary box producer
Only three races ago, after dominating the Turkish Grand Prix, Jenson Button described his Brawn as "a monster of a car, perfect, outrageous, the best I have ever driven".
You may have heard him on the radio during Sunday's Hungarian race, bewildered, saying: "How did this car get so bad?"
Give or take a few development parts, this is the same car he is talking about. Whatever has gone wrong?
It is a question the team need to answer quickly. Three races ago Button was waltzing his way to the world championship having lost only one of the first seven events.
Now, as he points out: "I've lost an average of five points a race to Mark Webber in the last three. At that rate he'll be in front of me in another four races - and there are seven still to go."
No smoke without fire? Brawn's tyre troubles could ruin their season
What is very clear is that the issue is to do with how the Brawn BGP001 uses its tyres.
The lack of performance in the previous two races, at Silverstone and the Nurburgring, was put down to the track characteristics and the cold weather combining with the car's characteristics to give sub-optimum tyre temperatures.
But the Hungarian race was held on a circuit with lots of long twisting turns, requiring lots of braking and - on a generally hot day - conditions that should ensure plenty of tyre heat.
Yet the team could see from their data systems that the tyres rarely got beyond 60C during Sunday's race, this being about 20C lower than they need to be in order to work properly.
There were moments during the race where the track temperature crept beyond 40C and at these moments Button would suddenly find grip and go quite quickly.
His best lap, set during one of these extra-hot spells, was only 0.2 seconds slower than the fastest set by the race winner Lewis Hamilton.
But usually the temperature of the surface would hover in the high 30s and in these conditions Button's tyre temperatures would fall back below the critical minimum and he would again be slow as the rear tyres grained.
The correlation was almost switch-like.
"We saw it also on Friday," stated Button after Sunday's grand prix. "The track was 10-deg hotter than during the race and we were in really good shape with the tyres.
"We had grip and we were getting fewer problems with the tyres than any other car.
Car 'is not what it was' - Button
"There was nothing different between Friday's car and today's. All that has changed is the weather."
The car is not loading its tyres hard enough to generate the necessary temperatures but the puzzling thing is how this tendency has been accentuated sometime in between the Istanbul race and the Hungarian one so that it is now apparent, even in conditions that did not bring it out before.
Team principal Ross Brawn added: "We have to unravel what we have done to the car in the last couple of races and understand if we've done something that has exacerbated the problem.
"It seems to have changed from where we were three or four races ago. At Monaco and Turkey we didn't have a tyre problem."
Back to the drawing board for Brawn (UK users only)
The forensic work of tracing all the updates and changes to the car and relating them to the tyre temperature problem is now hindered by the fact that F1 faces a mandatory two-week summer factory shutdown, this a measure introduced this year as a cost-saving measure.
"Yes, but I believe you're still allowed to think about F1," said Button mischievously.
It's good that he can retain his sense of humour about it all because whatever thoughts the team members can collectively come up during that vacation period could well determine the outcome of the world championship.
Mark Hughes has been an F1 journalist for 10 years and is an award-winning author of several books