Hi,
i assume a bug:
when you
use a vector shape,
fill it with white,
add a black outside outline (layer effects)
reduce the fill opacity
The fill gets darker and finally black (not expected).
Expected is fill gets transparent, but stays white. Instead, it gets the color of the outline.
When reaching 0% opacity, fill gets transparent (expected), but the outline is extended to the inside (wrong).
Spotted by my son in 1.8.5 and 1.9.0.932
Example file shows two linked vector shapes, one using stroke behaving correctly, one with outline mis-behaving. Linked so opacity affects both, and you can see the issue.
outline opacity issue.afphoto