it most likely was intentional. grey ninja can be like that. but he has some other redeeming qualities so we keep him around.

as grey was saying, you don't really need a case for your carts. you can buy cheap plastic cases if you want--i think both pelican and madcatz make some. they're usually in the neighborhood of a buck each. but they're totally unnecessary. i've never had a problem with a cart loosing data or becoming unreadable--this includes games for my snes, n64, gameboy, gameboy color and gameboy advance. only ones i've ever had a problem with were the original nes carts, but that was the fault of connectors getting dirty/worn in the system itself, not the cartridges.
i think you'd be better off saving your money on cartridge cases and getting a case for your sp. i've said it before on this forum, i highly recommend the case from madcatz. it's made of hard plastic so it protects the system very nicely. it also can hold up to 4 carts, so they helps in solving your cartridge storage problem. you can find it for something like $15, bundled with a car charger, headphone adaptor, and the cheapest pair of headphones ever made. worth every penny.