The variations are broken in WooCommerce 2.1.6. When you edit a variable product, the variation options gets cleared under the variation tab.
1. Add a color attribute, make it a variation, add colors: Green | Blue | Red
2. Go to variations and select "create variations based on attributes"
3. You will have 3 variations with one color each
4. Save the product
5. Make edits anywhere in the product, save again
6. The color settings for the variations will now be blank and need to be re-configured