It does appear that the value might be used without being initialised, but I haven't checked through each macro to be sure.magick/channel.c: In function ‘SetImageAlphaChannel’:
magick/channel.c:886:9: warning: ‘pixel.opacity’ may be used uninitialized in this function [-Wuninitialized]
Possible uninitialized variable
Possible uninitialized variable
Re: Possible uninitialized variable
We can reproduce the problem you posted and have a patch in ImageMagick 6.9.0-9 Beta, available by sometime tomorrow. Thanks.