The problem may be the orientation of the tilt sensor in your guitar controller, not a glitch in the game.
The cheapest way (money-wise) to combat this problem is to try positioning your controller (for example: neck pointing slightly downwards) at different angles. It's a trial-and-error process and can be potentially time-consuming.
I've had a similar issue where one of my guitars would activate Star Power when I didn't want to use it yet. I slightly pointed the neck towards the TV and the problem was gone.
Here was how I used to play: me -->| |<-- TV
Here is how I play now: me -->/ |<-- TV
Hope this helps a bit.