Kopete outputs all received and sent messages to the output, which on Linux desktops is by default captured in ~/.xsession-errors and thus logged more or less permanently: ... kopete(10161) squashMessage: "*secret text*" kopete(10161) squashMessage: "*secret text*" kopete(10161) squashMessage: "*secret text*" ... This happens even in OTR protected communication, where messages by default should not be logged. The OTR plugin should suppress the printing of these messages or at least make only a placeholder text show up.
Those are just debug output outputs for area 14000 (Kopete). You can enable/disable debug output in program kdebugdialog. IIRC it is configured in kdebugrc config file and Linux distributions provides its own config files. If you have enabled those debug outputs for Kopete by default (verify via kdebugdialog), then please report this problem to your Linux distribution. Closing now as downstream.