Most problems like you describe are caused by a dodgy earth, try taking the brake light bulb out and seeing if i still does it, if it doesn't it's in that circuit, could just be a dirty bulb connection
What I meant to say is that I saw an 08 GS1200 yesterday morning and whilst his indicators looked like the OE type as soon as he put his brake on the indicators also lit up along with the tail lamp. The red light they gave off was very bright like an LED