Confusion re: futurize and "Files that need to be modified" with "No changes"

[bhrutledge]

I'm confused this output:

$ futurize --stage1 module_a.py
RefactoringTool: Skipping optional fixer: idioms
RefactoringTool: Skipping optional fixer: ws_comma
RefactoringTool: No changes to module_a.py
RefactoringTool: Files that need to be modified:
RefactoringTool: module_a.py

Specifically, that there are Files that need to be modified, when there are No changes. On another file:

$ futurize --stage1 module_b.py
RefactoringTool: Skipping optional fixer: idioms
RefactoringTool: Skipping optional fixer: ws_comma
RefactoringTool: No files need to be modified.

I can't share the specific code where I'm seeing this, and I haven't tried to come up with a shareable version. Before I start that process, any thoughts/suggestions?