In Irssi, "the client of the future", the input box behaves differently by default from the input box in other clients, for example XChat. In XChat, each window or tab has it's own input buffer, so you can draft a statement in one window while still conversing separately in other windows. In Irssi, the default behavior is to for there to be only one input buffer, which persists as you change windows.
To get a separate input buffer for each window (while still pooling the input history), see this script.
