Alcyone center tail light?

I have a similar problem. I wired up mine myself. The `blank`panel they put in the UK cars can easily be removed with some paint remover and some gentle rubbing. I thought I had done a pretty neat job until someone told me that It does work as a brake light but also flashes when an indicator is put on.I.E. If you are braking and indicating at the same time( if slowing down at a juction for example)then it will flash with the indicators. It works perfectly if braking normally. How can this be ? All I did was to wire into the stop/tale wire, which is nothing to do with the indicator wire!

Any Help on that one!

Rich.