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In a player vs player local Commander game, I encountered a bug where Krow plays a Negate from hand to counter Brittany's Cast Out. When Krow cast the spell, it wouldn't let me tap his lands to pay for it, and when I pressed "Auto", it tapped two of Brittany's lands and attributed Brittany as the caster. The Negate, as seen in the screenshot, was then properly put into Krow's graveyard.

I'm playing Forge v1.6.18 on Windows 7 with Java 8 JRE 1.8.0_161