I mainly saw this problem in my clients associated with "jerky" casting. Abrupt starts and stops instead of "smooth acceleration" through the casting stroke. The more you practise and the smoother your casting becomes, this will go away. All the links above to video's are great.
Think of it this way. Once you have cast the line, you have to wait for it to arrive at it's target. Once it's there you can pull back (in the opposite direction) slowly until it's tight, and when it is, you can then accelerate to toss it back the other way.
Some of the best casters I have ever seen live right in calgary and fish the bow. If you see someone casting nicely, stop by, say hello, and ask to watch them for a while... watch the rod tip and position and not the line as they cast. Should help ya