In recent memory, only the Mercedes CLR and Porsche 911 EVO were flippers in the GT1 category. However, the BMR LMR also did a backflip at the petite LeMans, in the exact same spot the Porsche 911 EVO did.
There are a lot of contributing factors to it; it's not just the crude aerofoil shape of the GT1/GTP profile. It also had to do with the centre of downforce being so close to the rear, and soft rear springs which amplify the effect. There's more, too, but I can't remember it all. There's an interesting artciel on Mulsanne's Corner about it for those interested. Ultimately, these backflip phenomenon spawing the new ACO rules (2005 was it?) with the longer noses, shorter tails, smaller rear wings, shorter rear diffuser, longer front splitter and diffuser, chamfered floor, tunnel section, and the raised nose. It was all an effort to move the centre of downforce further forward. It was also intended to have the effect of increased drag to slow the cars down. Ironically, some teams found increased downforce, reduced drag and ultimately lower lap times from these changes.