Hmm, I can't reproduce the bug anymore... The machine had to be rebooted over the weekend (it is a server at the company where I'm working) and now top's output is all right again:
Tasks: 86 total, 1 running, 85 sleeping, 0 stopped, 0 zombie Cpu0 : 0.1% us, 0.2% sy, 0.0% ni, 99.5% id, 0.2% wa, 0.0% hi, 0.0% si Cpu1 : 0.1% us, 0.1% sy, 0.0% ni, 99.8% id, 0.0% wa, 0.0% hi, 0.0% si Cpu2 : 0.1% us, 0.1% sy, 0.0% ni, 99.8% id, 0.0% wa, 0.0% hi, 0.0% si Cpu3 : 1.2% us, 0.0% sy, 0.0% ni, 98.7% id, 0.0% wa, 0.0% hi, 0.0% si Mem: 2075860k total, 141680k used, 1934180k free, 29008k buffers Swap: 2634652k total, 0k used, 2634652k free, 52388k cached So I suppose you can close the bug. If top's weird behaviour will come up again, I'll reopen it. Thank you Adalbert