I have a new Spider Classic as well. It WAS clean for the first couple of weeks, but now every time I turn it on, I've got funky effects in clean mode.
Here's the solution (Through simple experimentation and logical process):
Turn effects knob A all the way up and then off. Then turn effects knob B all the way up and then off.
Effects are now actually off.
Not sure why it works like that all of a sudden, but that's the simple solution.
I've noticed too lately that my volume knobs seem to have only 2 settings: Off and Shake-The-World. With nothing in between no matter how I set them. I'm probably doing something wrong, but I can;t help but wonder if this is somehow connected to the effects issue.....