STEPS TO REPRODUCE
1. Launch iClone 6
2. Apply a random Particle content
3. Navigate to Modify > Edit > Particle Settings > Particle Key > Color, 4 triangles displayed
4. Select color 1, drag the slider for Opacity to 31
5. Select color 2, then click color 1 again

ACTUAL RESULT
The Opacity value for Color 1 is changed back to original

EXPECTED RESULT
For Particle Key, if click another key, the value of the previous key will be kept