I understand from many tutorials that GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA is the best blend function.
(which makes perfect sense, 1a-1a = 0a)

Anyway, all blend functions seem to work as their documentation says they should except that one. When I use that one it doesn't use the alpha channel.(replaces it with black)

Is there any common reason for this problem?

This is mainly for particles & HUD elements.