Well, "priming sugar" is just corn sugar (dextrose) but not plain old table sugar. I think that there is a difference in the amount you would use, as well as flavor.
I boil 2 cups of water and add 4 ounces corn sugar, and then cool it and rack my beer into it. It's important to mix well without aerating, so I put the tip of the hose in the bottom of the receiving bottling bucket so that it "swirls" to mix well without splashing or stirring.
If you didn't mix it well, it could be that some bottles got more sugar than others.
Or did you add a measured amount of sugar to each bottle?