CHICAGO (Reuters) - After Russia's invasion of Ukraine sent global wheat futures soaring, U.S. farmer Vance Ehmke was eager to sell his grain. Local prices shot up roughly 30% to nearly $12 a bushel, about the highest Ehmke could recall in 45 years of farming near the western Kansas town of Healy. Instead of reaping a windfall, Ehmke found a commodities market turned upside down. He and his wife Louise told Reuters they couldn't sell a nickel of their upcoming summer wheat harvest for future delivery. Futures prices for corn and wheat had rocketed so abruptly that many along the...