The bug

When using Caret notation (^a ^b ^c), Command blocks always "face" south no matter what their "facing" data is set to.

This is almost more like a feature request than a bug, but I do think the behavior is slightly unexpected. it works fine if you're using Execute or any command that involves an entity, but if you're using a command that doesn't use an entity, there's no facing vector for use in ^-notation, so it defaults to south.

How to reproduce

1. Create a command block with facing:east 
2. Set its command to "/setblock ^ ^ ^1 stone"
3. Power the command block
4. Unlike an entity performing the command, instead of placing the block one space to the east, it will place it one block to the south

Reasoning

1. It makes intuitive sense that a command block should use its facing vector for caret positioning. 
2. It makes it easier to build systems that require caret positioning because you can point the block in the direction you'd like to effect
3. Some constructs become less direction-dependent. when recreating a command block structure that uses this feature, you don't need to worry about what rotation you've built the machine