Command block ignores radius requirements when far from 0,0,0

To reproduce:
Place a command block
Set it's command to "say Found @a[[x=<large number>,y=0,z=0,r=1]]"

If <large number> is big enough, it will ignore the radius limit and say the name of everyone present. The exact number where it breaks seems to be different from world to world, the smallest number I have seen being 27946 and the largest somewhere around 3.5 million.

It works in both single and multiplayer, but the breaking point seems to be smaller in SMP.

(I've also noticed a trend where the breaking points are smaller in worlds with bigger world IDs, so the nether will normally break down sooner than the normal world, and a modded smp 5th world will have a smaller number than that. I don't have many datapoints though, so this might not be real.)