During the course of investigating a bug that resulted in the system crashing with a bluescreen, the question arose, "What are the compatibility consequences of making this change? Are there any legitimate scenarios where somebody would be relying on being able to do XYZ and counting on the old behavior?"
I had to step in and state the obvious:
"There is clearly no valid scenario for the old behavior, because if you try to do XYZ, you crash with a bluescreen."
Some people were amused by the clear logic of this statement. But it's also the case that sometimes people get so excited that they miss the obvious.