RJ's right, in an FF car running stiffer springs at the rear and softer at the front is normal, (learnt that from tuning the Golf and common sense of the knowledge of weight distribution). It could be in this car that because of the light-weightedness (it must have a light engine) when you use a stiffer rear most of what weight it has is placed on the rear tyres WHEN TURNING and the front loses too much grip to turn properly. Normally an FF understeers also because of the weight of the engine
and diff being up front and nothing is out back, (as well as the fact that weight transfers backwards under accleration and the tyres up front lose grip). But the engine is so light in this car that it doesn't have much weight there in the first place and using a stiffer rear suspension puts more weight on the rear tyres when cornering (normally you need this to balance an FF car's weight and help it turn) and results in a lack of grip for the front tyres. So in conclusion the combination of accelerating through a corner and more weight transfer onto the rear tyes and stiffer rear springs also resulting in more weight on the rear tyres means that the car has little weight left to get the front tyres to grip with. Normally in an FF car this is not a problem as there is a lot of weight up front when cornering and using the stiffer rear springs removes some of that creating better balance and therfore better handling.
Just my 2 cents, and I hope I'm right otherwise someone will have to correct me. I may have repeated myself a couple of times to get a point across, sorry about that. It makes sense to me, does everyone else understand it?
Here, I got an idea, I'll try and show what I mean through use of number diagrams just like in Greyout's guide to weight transfer. I will show the difference between 2 theoretical FF cars weighing 1000kg, one is the Spoon Civic and one is a normal stereotypical FF. The diagrams show the amount of weight on each tyre and are not exact accurate readings, but give the idea I'm trying to put across. The front tyres are the numbers up top of each diagram, and left tyres are on the left and right tyres on the right.
Spoon Civic
Stereotypical FF
Weight on tyres when car is sitting still
300 / 300
350 / 350
200 / 200
150 / 150
Note that the Spoon's engine places less weight on the front as it is lighter
Weight on tyres when accelerating
150 / 150
200 / 200
350 / 350
300 / 300
See this explains why the Spoon also get more wheelspin, less weight there when accelerating. Both cars shifted 300kg backwards.
Now assuming we have stiffer rear springs
Weight on tyres when turning right
150 / 300
200 / 350
200 / 350
150 / 300
See how when turning with stiffer rear springs the Spoon has less weight on the front wheels than the conventional FF, therefore the normal FF has actually got more grip and weight on the front tyres than the back meaning less wheelspin while turning than the Spoon. The reason the sterotypical FF has less weight on the rear is because of the heavier engine still. Obviously when cornering you aren't full bore accelerating, but you are a little. And the balance is good for the stereotypical FF here, and the Spoon for that matter but the balance is better for the normall FF.
Now let's go stiffer front springs at the front
200 / 350
250 / 400
150 / 300
100 / 250
See now the Spoon has more weight on the front and gets less wheelspin while having a better balance and therefore more neutral handling than the sterotypical FF. The sterotypical FF will have way more traction than the Spoon in corners but the balance is way off and will have so much weight at the front it will understeer. Mind you at no point is either perfect- they're still FF!
And also having stiffer front springs will still hurt straight line acceleration traction but in corners it will be better for the balance and traction so that's why this car is better with stiffer front springs So there you go =drifting24/7= Your stiffer rear springs had good basis in theory and will still work in a straight line (or a normal FF) as it will limit lift off the front tyres in a straight line but this car is unique and stiffer rears will not help handling here.
and tuned.. well, it vanished to horizon.
)
.., 
