No, its not normal - unless you live in the south and have been suffering drought like the rest of us, when you could say it was normal - its the tree's reaction to severe drought.

Mine flowers in the spring, then grows leaves and sets seeds. Then in the fall it will put out new flower pods, loose its leaves, and wait for spring.

Bamboo's spot on, and I expect this year's exceptionally dry conditions have precipitated the early leaf fall. It'll be okay, I expect, because of recent rainfall, and will be back to its vigorous normal self next year.
Phil J