Particles - disappear with increasing lifetimeMS?

I've run across a problem where as the lifetimeMS increases, the particles begin to become more fadey....

For example, this sample datablock (from my modified crossbow):

datablock ParticleData(CrossbowBoltParticle)
{
   textureName          = "~/data/shapes/particles/smoke";
   dragCoefficient     = 0.5;
   gravityCoefficient   = 2.0;
   inheritedVelFactor   = 0.0;
   [b]lifetimeMS           = 750;[/b]
   lifetimeVarianceMS   = 10;   // ...more or less
   useInvAlpha = false;
   spinRandomMin = -0.2;
   spinRandomMax = 0.2;
   


   colors[0]     = "0.2 1.6 3.3 9.1";
   colors[1]     = "4.2 2.5 6.1 1.0";
   colors[2]     = "2.0 4.0 2.0 9";

   sizes[0]      = 0.2;
   sizes[1]      = 0.2;
   sizes[2]      = 0.2;

   times[0]      = 0.2;
   times[1]      = 0.5;
   times[2]      = 1.0;
};

would show up ok, while this datablock:

datablock ParticleData(CrossbowBoltParticle)
{
   textureName          = "~/data/shapes/particles/smoke";
   dragCoefficient     = 0.5;
   gravityCoefficient   = 2.0;
   inheritedVelFactor   = 0.0;
   [b]lifetimeMS           = 9000;[/b]
   lifetimeVarianceMS   = 10;   // ...more or less
   useInvAlpha = false;
   spinRandomMin = -0.2;
   spinRandomMax = 0.2;



   colors[0]     = "0.2 1.6 3.3 9.1";
   colors[1]     = "4.2 2.5 6.1 1.0";
   colors[2]     = "2.0 4.0 2.0 9";

   sizes[0]      = 0.2;
   sizes[1]      = 0.2;
   sizes[2]      = 0.2;

   times[0]      = 0.2;
   times[1]      = 0.5;
   times[2]      = 1.0;
};

would have the particles reeeeaaallly faded. (Notice that the only difference between the two is the lifetimeMS: 750 compared to 9000)

I'm guessing this is probably done to prevent the memory from being overused - if it is, is there a 'hack' for this?

If not, is anyone else having this problem?


EDIT:

Oh yeah, just in case it might be a memory thing, I have ~400MB RAM, 1.4gHz, and a somewhat-poopy graphics card built into my laptop