The bug

Caret notation (^ ^ ^) can be used in all commands to move the effect relative to the direction an entity is facing. For example, /summon cow ^ ^ ^3 creates the mob three blocks in the direction the player is viewing, starting at their feet. This works as intended.

However, when used in execute or detect, the view direction is not used and the coordinates function exactly the same as if they were ~.

How to reproduce

Face a diagonal direction and run this command:

/execute @p ^ ^ ^5 summon cow

→  The cow was summoned five blocks south instead of five blocks forward.