I don't know if it's a known issue or even a know limitation as of now but as i was trying to do a believable dirty glass shader i thought i would try to blend an architectural, single faced glass material with a simple diffuse material.
But it seems that, although i have no problem mixing those 2 together, there is no transparent shadow anymore, making this combination a "no-go", unfortunately.

So perhaps am i late to the plate (more than probably) but if it wasn't discovered already i hope this little explanation, as well as an image demonstrating the problem and the scene file to go with it, will help squash this annoying behavior, if it's possible of course.

Thanks for reading,
Cheers,
Laurent aka Tartiflette.
