Checking the Mute previous clips" button causes SONAR not to start recording!

So I set up my rig to record. Everything works fine. Eh.. except the audio punch facility. I set it to "mute previous clips" and it just refuses to obey the record button on the large transport. This button would not turn red and would not record.

Well, audio recording goes on smoothly if I then uncheck the "mute previous clips". So I got round this by manually muting previous clips to enjoy the agony of hearing previous clips!

Any suggestions to overcome this - eh, apart from re installing SONAR?