Problem with alpha channel shader

[mongoose7]

Dunno. TRANSPARENT_ALPHA_CHANNEL is usually used with a separate transparency map. Probably you should have used EMT_SOLID.

[jimy-byerley]

Yes, I just tried and EMT_SOLID is working too. But with EMT_SOLID, transparency has sometimes problem and is rendered with the background only and not other objects.
EMT_TRANSPARENT_ADD_COLOR now works too as expected (but I won't use it for clouds !).