When I start Netbeans I can edit text. I put the focus on another window (Thunderbird for example). After returning to Netbeans keyboard input is not accepted anymore. I can mark text with the mouse.
Keyboard input is only recognized after I click on another tab in Netbeans and then return to my former tab.
Any help would be greatly appreciated.

I run Kubuntu with KDE 3.5. SCIM for Japanese input is installed.