According to these results, your random colors consists of only 4 different colors? Either this is true, or my alias is somehow picking up the wrong values. Not only that, but the 4 colors showing up as being in the palette are obviously coming from other rules down below, and none of the colors listed in the palette are coming from the random colors.

Can you confirm which mIRC version you're using?

And can you confirm that you're seeing more colors than just the 4 in your debug message?

Even if you edited your color scheme to have all the colors 0-15 being identical, there should be lots of other colors in the 16-98 range showing up in your colorized nicks.
The only way I see that this should be happening is if you have a script using /cline to change the color of these nicks away from the random colors, but something like that shouldn't be triggered by opening the colors dialog.