...but i think it should be fixed
If you have set nicknames colours in the "nick colours" dialog (the one in alt+b) and you MANUALLY (with /cnick) add THE SAME entry, mIRC doesn't check if the entry exists, so you end up with two exact entries.
for example I have channel ops coloured in light green (colour 9), only in listbox, and I do
/cnick -m2 * 9 @ => it adds exactly the same entry
if I do /cnick -m2 * 8 @ I end up with two different entries, while the point IMHO is to EDIT the existing entry
another thing is that /cnick misses switch/parameter which allows to prioritise the entries, but this goes to another forum