Edge detection callback fails silently after upgrading RPi.GPIO to 0.7+

Context

An existing Python script uses RPi.GPIO edge detection callbacks to monitor a button press on GPIO 17 (BCM). After upgrading the library from 0.6.x to 0.7.1, the callback function no longer executes when the button is pressed, even though the script starts without errors and the pin reads correctly via polling.

Goal

Determine why the falling-edge callback registered with GPIO.add_event_detect() stops firing under RPi.GPIO 0.7+ while the same code worked on 0.6.x.

Constraints and uncertainty

• The script sets GPIO.setmode(GPIO.BCM) and configures the pin as input with pull-up.
• No exception is raised during add_event_detect() or add_event_callback().
• Changelogs mention internal threading changes in 0.7 but do not detail callback signature requirements.
• Downgrading restores functionality, confirming the hardware and wiring are correct.

Questions

1. Does RPi.GPIO 0.7+ require a different callback signature or explicit thread-safety handling for edge callbacks?
2. Is there a documented migration step for add_event_callback that was omitted from the release notes?
3. Can the callback be made to work without reverting to polling or downgrading the library?