JEM 7DBK - why 4 trem springs?

[pseudomarine]

Guys - I know that this isn't exactly rivetting stuff, but...

I removed the back plate from my 7DBK to get at the trem. I noticed that there are 4 trem springs.

Usually I'd expect to see 3 springs, but on my trem there's a 4th spring between the middle and bottom springs (where the bottom spring is that closest to the ground when holding the guitar normally). Also, just as a bonus, the bottom spring is black, not silver.
All the springs are linked horizontally from the claw straight to their corresponding hole in the trem block.

does anyone know why? I'd have thought that the tuning would be unstable due to this configuration of springs...

Cheers

[Gresh]

What gauge strings are on it?

It wouldn't necessarily make it unstable but someone would either have to have put fatter wire on it or backed out the trem claw screws to compensate for the added tension the extra spring is causing. It would make for a more "stiff" feel that's for sure, not something I would like at all.

I'd pull it off and redo the set up.