Inconsistent behaviour when scrolling volume slider with Magic Trackpad

[18571728]

Inconsistent behaviour when scrolling the volume slider with Magic Trackpad and "natural scroll direction" enabled.

Prerequisites:

1. Attach input device: Magic Trackpad

2. System Preferences, Magic Trackpad, Enable "Scroll direction: Natural"

Built-in volume slider for reference:

A. System Preferences, Sound, Enable "Show in menu bar"

B. Move cursor to the System Volume item in the menu bar

C. Click the Volume item and move the cursor over the volume slider

D. Slide two fingers UP on the Magic Trackpad and notice that the volume slider goes UP

Conclusion: sliding UP makes the volume slider go UP.

Spotify volume slider:

i. Move cursor to the Spotify.app player volume slider located in the lower right corner

ii. Slide two fingers UP on the Magic Trackpad and notice that the volume slider goes DOWN.

Conclusion: sliding UP makes the volume slider go DOWN.

Expected: I would expect the Spotify volume slider to behave in the same way as the built-in volume slider.