Transparency < 50% = Invisible. Why?

No problem with transparency (material->blend=SIO2_MATERIAL_COLOR) if a face is uv-mapped to an area of the png where transparency is > 50%.

But, if mapped to an area where transparency is < 50%:

The face won't render and shows up as invisible at run-time.

- Not using SIO2 lighting.

* Could this be is a problem with the ->specular, ->diffuse, or ->shininess properties of the material type?
* What are the max/min values for those properties and how do they correlate to blender-style settings like Reflectivity?

Anyone have any ideas on this? Thanks.

Have you set an alpha level?