Ok I had the same problem last year. Fitted a new module and was fine... After a lot of head scratching I found the coil firing after TDC. I checked the magnet for shifting, all ok.

The new module I fitted still used the old pick up... I bench tested to whole unit, when I used the new pick up as in normal opperation the spark was retarded, turned it the other way (Hall effect) It was now firing BTDC..I refitted the system and did a few flights untill I had a dead stick..Same problem, rotated the hall effect and was now BTDC..I tried the old hall effect and the problem was gone..... I couldnt work out what was going on and had no trust on the module. It went to the bin and the RCEXL stayed... God knows what goes on with cheap Ignition modules....

So For your answer..It happens..