alpha issues with architectural material

[cryptosporidium]

hi, have anyone experienced problem with rendering correct alpha of refractive architectural material? sometimes it works, but in some cases it doesnt and i couldnt figure out why. my test scenes were rather simple, just one lowpoly object with glass like refractive arch mat so there wasnt much space to screw something up. alpha consider object boundaries, but it doesnt render transparecy of the material. any hints?

[Zac-Donald]

maybe you should try ray tracing vs scan line? I really don't have any idea though, just something you could try.

[cryptosporidium]

i found out its probably a bug here. seems like "no alpha" in background means "non-transparent alpha" for arch mat, therefore if you render against empty background, it renders everything full white. But if you put any picture with black alpha in the background, you basically force arch mat to adopt alpha from the background image (which is transparent) and everything now works as you would expect to.