large number of applications on iPhone 3GS leads to slowdown

Hello all.
Since release of iOS 4.2, Ive started facing strange bug. Enabling rearrange icons on springboard feature takes about 5-7 seconds! That feature which helps you move icons across springboard or deleted applications.
Ive checked clean 4.2 (restoring iPhone, didnt restore apps from backup), same bug.
After 4.3 rolled out, Ive expected that this will be fixed, but of course it doesnt. Again Ive restored iPhone to 4.3 without restoring all apps from backup to check it. And found that there is no such bug! Cool. Mentioned above feature works as expected. But after restoring everything from backup (I have about 320 apps), the bug reappeared again.
So, is this because I have to many applications installed on my iPhone, or this bug can be fixed by Apple?
Any ideas or may be solution?
Thank you
3GS iOS 4