Cali 1100i no spark

Whilst trying to overcome a no spark problem I noticed that when I switched the ignition OFF there was a spark at the plug. Any ideas what this could signify?
My ecu was swopped to another cali and it fired up and idled just fine…put it back in mine and zilch . This is driving me nuts!

Suggestion - disconnect and remove the phase sensor. Examine it carefully - if it is in the least bit barrel shaped get a new one. Chances are if it is difficult to remove then it has swollen up internally and the resistance will break down as it sees power. I believe the item is readily available from various places. My Sportie 1100 had a similar issue which drove me nuts because it would fire up, warm up, break down, then splutter to a halt.
I found these people very helpful:

Of course, it may not be that component at all. If you can swop over the other 1100i sensor to check then that would be useful before the expense of buying a new one.

edit: There should be a resistance figure in the workshop manual somewhere for this item - a quick check with a multimeter might shed some light.

Found the same problem on a 400/4 before the war. It had a Piranha electronic ignition system and after an engine out job it refused to start and switching of the ignition switch it produced a massive backfire with a huge flame out the silencer. The upshot was my mate had nipped the trigger wire from optical chopper system. Made good the wiring and it started 1st touch of the button. Hope this helps.

Thank you for your advice re difficulty in removing phase sensor, I had difficulty removing camshaft sensor whereas the crankshaft one was easy.
I replaced the camshaft blighter and ‘spark city’ . I had it running today so I am a very happy chappie.
So good to hear the thing roar into life.

Mille grazie tutti