It's classic "double-spending" - sure, I'll sell you my GPL-licensed DB! For millions of dollars? Absolutely! Sold!
I quit! Now let me fork the thing I just sold to you and keep developing it for free-as-in-beer and free-as-in-freedom.
Sigh. Silly multi-billion dollar multi-national corporation! I'll be really impressed when Monty Widenius sells MariaDB to Oracle. And then quits.