WooCommerce Composite Products Trying to set SKU on Variation gives "Variation SKU must be unique." error

I just learned how to create a variable product, and it mostly works, even showing up on the webpage with the proper variations in the dropdown list. Each variation does have an sku #, but when I try to plug that number into the SKU field for each of the two variations, and then click "Save" (and then update the product), I get an error message for each variation, outlined in a red box, saying :

7210 – Variation SKU must be unique.

7209 – Variation SKU must be unique.

The SKU numbers for each variation are unique. I don't have any products with those sku values on the Products page.

Screen shot of the event, showing both variations, their prices, and the sku numbers I'm entering (note: upon saving & updating the page, the sku numbers will clear from the sku fields, I presume because the plugin thinks they aren't unique sku numbers?)

via Chebli Mohamed