I honestly wouldn't put much faith in anything you read on paintball.com. I don't think much of that site at all.
Dry ice is frozen carbon dioxide. A block of dry ice has a surface temperature of -109.3 degrees F (-78.5 degrees C). Dry ice also has the very nice feature of sublimation which means as it melts it turns directly into carbon dioxide gas rather than a liquid.
At normal pressures, carbon dioxide moves straight from solid to gas. Sometimes when you fire a gun shooting co2 you will see 'snow flakes' these are dry ice.
You see dry ice because this is liquid co2 from your tank at normal pressures (atmospheric). It is only at much higher pressures that you find liquid carbon dioxide. For example, a high pressure tank of carbon dioxide such as we use in paintball contains liquid carbon dioxide. The co2 in your tank is stored at approx 850psi and at this pressure the gas is constantly changing phase from liquid to gas. As you use up some of the gas in firing a shot, more of the liquid changes to gas to keep the pressure the same.
There is no problem in having liquid co2 in your tank. Indeed if you are to have a proper fill in your tank it must have liquid in it. There is no need to worry about getting 'dry ice' in your tank.
The only things to be careful about are overfilling, in which case the pressure can get to high and cause a rupture, and leaving the tank in the sun, in which case the pressure can get too high and cause a rupture...
(it should always blow the burst disk first though!)
Make you sure you weigh your tank carefully when filling it and keep your gun out of the sun whenever possible and you will be fine.
manike