The Alfa Romeo team's tyre mistake that compounded Kimi Raikkonen's "sh**" Italian Grand Prix weekend was a misinterpretation of the Formula 1 pitlane start rules.
After crashing at Parabolica in first practice at Monza on Friday, Raikkonen made the top 10 in Q2 only to have a second accident at the same corner in the final part of qualifying.
The team was forced to change the gearbox, earning him a five-place grid penalty, and also took the opportunity to upgrade him to the latest Ferrari Spec 3 engine.
Because that decision entailed a change of specification from the Spec 2 he had used in qualifying, Raikkonen was relegated to a pitlane start.
Alfa Romeo mistakenly thought that a pitlane start forfeits the obligation for drivers who make Q3 to start with their Q2 fastest lap tyres, and switched him from his set of used softs to a new set of mediums with the intent of gaining a strategic advantage.
But the Q2 tyre rule still applies to a pitlane start unless the chassis has been changed, which was not the case on this occasion.
The offence was reported to the stewards, who were obliged to give the mandatory stop/go penalty.
Raikkonen eventually finished 15th.
"Well that was a shit weekend," he said. "First my mistake in qualifying which unfortunately meant that we had to change gearbox.
"Then we decided to also change engine and start from the pitlane, but we had the wrong tyres on and with the penalty my race was more or less over.
"Looking forward to Singapore, as it can't get worse."
Alfa Romeo boss Fred Vasseur said on Sunday night that he did not yet know how the rules misinterpretation had occurred and would "need to investigate a little bit".
He backed Raikkonen over the qualifying crash, saying the tight margins in the upper midfield meant his driver had to give it everything in Q3.
The red flag for Raikkonen's accident prompted the late-session rush that ended in huge controversy as drivers backed off trying to avoid giving a slipstream to rivals and mostly missed their final flying laps.
"Sometimes a small mistake at the beginning can create a huge mess," Vasseur told Autosport.
"We have to stay calm on this. He did a great job from the beginning of the season.
"We know perfectly if we want to do a P6 or P7 in quali we have to take a lot of risks, and we have to accept doing some risks that you can do some mistakes."