Some of the flavoring got absorbed by the plastic, just as strong flavors of leftover foods (onion, tomato, lemon, etc.) get absorbed by plastic containers. You'll barely taste it the next time you use the bottle, and after three or four uses it'll dissipate. Heed seems to be particularly persistent, but all sports drinks (and fresh squeezed lemon juice, for that matter) will get absorbed by the plastic.

I don't like to use bleach because of the dioxin, but if bleach-based dishwashing detergent is what you like to get the smell out of your bottles, then a weak solution of bleach should work on your Camelbak bladder as well. But as I said, it's unnecessary.