values between 0.0 and 1.0 works as it should, but values between -1.0 and 0 works very odd and can been very confuction to been used the right way.
By now -1 and 0 is the same, but -1 should been blank and not a value close to 0. Its simply seen the command do the other way as its should.
Normally 0 should been the middle point, so 0 is normal, -1 is completly off and 1 is lightest.
This would been much easier to understand.
PS. I known there is a workaround by creating a SETALPHAMODE function and do the math here, but for me its still a bug.
It's always been like that - its strange but you soon get used to it :)