I've managed to make several 306s oversteer...lifting off or braking mid corner has that effect. 
As do shit 'snappy' tyres like T1R's.
Also if the tracking is as far out as it was in Rowells estate, that can also cause pretty bad oversteer, followed by massive over-correction and the need for fresh underwear.
Over-inflated rear tyre's also cause problems if theres no weight over them (empty fuel tank for example), has the same effect as stiff rear shocks, which are crap on rough roads, massively reduces tyre contact patch.
As do shit 'snappy' tyres like T1R's.Also if the tracking is as far out as it was in Rowells estate, that can also cause pretty bad oversteer, followed by massive over-correction and the need for fresh underwear.
Over-inflated rear tyre's also cause problems if theres no weight over them (empty fuel tank for example), has the same effect as stiff rear shocks, which are crap on rough roads, massively reduces tyre contact patch.