After not making any changes to the items that broke after only two installation laps on Tuesday besides replacing some parts, the McLaren Formula One team had an inexplicably drama-free day, reports . Wednesday was the car’s best run all year, and McLaren has no idea how or why their car didn’t break. Incredible!

McLaren driver Stoffel Vandoorne set the fourth fastest lap of Wednesday’s test sessions and was able to cram in a full 81-lap day of testing for the team with zero problems at all with the car’s problematic Honda power unit.

It’s a welcome reprieve for a team that’s done little but break down all year, however, they’re not sure what to do with this whole “working car” concept—mostly because they have no idea why the same exact spec that failed is all of a sudden working. McLaren racing director Eric Boullier told Motorsport.com:

[I]t is very difficult to understand what went wrong. We obviously changed the MGU-H I think, and yesterday morning after two laps the MGU-H was gone.

We changed the engine and did 17 laps yesterday, but we couldn’t find anything wrong physically on the car. So I think it’s going to be complicated for Honda to understand what’s wrong.

It’s maybe coming from a batch problem, maybe some anomalies are car related… there is no common cause.

Whatever caused Tuesday’s big failure is still a mystery. Obviously, they could still figure out what specifically failed after a full tear-down, as Toyota did after last year. Either that, or perhaps the same issue will reappear after more use. It’s like Honda Engine Roulette.

Either way, we’re so used to McLaren’s car not working that it’s bizarre news even to the team when the car isn’t broken.