I came across this problem by using a color-system. I tested the ctrl-k option on a basic mirc without any addons and came to the conclusion that there is a big bug in the color index.... By using almost any code followed up by a singel number (1-2-3-4-5-6-7-8-9-0) there will be send nothing to the chat. By pressing 33 on a color code, it wil send 3 to the chat. I think this is a real big bug and should be looked for by the creator(s) of Mirc.