[BUG] Alpha Channel in Envelopes

I recently encountered a bug in envelopes.

When the alpha channel of an envelope is exactly zero, or very slightly below or over zero (don't know), the graphics suddendly gets 100% opaque instead of vanished.

I encountered this bug by trying to hide stars during the "day" of a level, when I was a bit messy at pointing the points at exact values (which btw. often near to impossible) , the linear curve went from say -0.05 to +0.06. Now in the middle of the day the stars suddendly went 100% opaque for a while, possible when the float went through "exact" zero. (As far there is anything exact at floats :-) )

Request to be fixed when convenient.

BTW: Are any values below 0 and above 1 reasonable in color envelopes? This could IMHO also be restricted in the editor...