Its doing what Butterfly Bushes do: growing long shoots and then flowering. You don't need to cover it in your zone; they are hardy even here in Reno. The large growing ones can reach 10 feet tall in just a few months in warm climates. Your's is looking very typical to me. You can cut it down to about a foot tall every winter and let it regrow in the spring - otherwise, in a couple years, it will eat your entire yard.
If your other Butterfly Bushes are not exhibiting this growth habit, it means they are different kinds than this one. Some are very neat and tidy and grow to just 5 or 6 feet. Some, like Royal Red, get huge.
Daisy
