This is how things work now in KDE SC 4.6.1, I believe. As this is the same behaviour I see on my Kubuntu 10.10 box and my Arch Linux box, both running KDE 4.6.0 and 4.6.1.
Double-click on the tab to bring up the "Rename Tab - Konsole" dialog. This dialog has two separate input fields, one for local processes and one for remote processes.
You can clear the local field (Tab title format) and then just type whatever you want into it. Clicking OK will set the name of the tab to that text. If you connect to a remote system via SSH, the tab name will change.
If you absolutely want the tab name to remain the same at all times, then enter the same text into box fields.