When I'm using the /speak to output some text, it writes a line to the server console, saying what was spoken. It doesn't add a timestamp to the beginning of the line though, like everything else does. I'm not sure if this is really a feature though, as I don't know if /speak is working as intended. Maybe it's a bug? I didn't see it listed in the bug report section. I'm using mIRC 7.43, btw.
