I’ve been using Kopete on my quest to convert to KDE, and I’ve been extremely annoyed by previous conversions showing up in my chat windows. The option to disable it didn’t seem to be anywhere, but I found a forum post that pointed me to the Plugins section of the configuration.
Just disable the plugin entirely or open it and mess with the configuration. Things like that shouldn’t be on by default, along with chat window tabs (when did this become common?) and annoying buttons for fonts and emoticons. But, maybe I’m more minimalistic than many.