I am getting error messages from -fx in everything I have tried. For example, the simplest is:
convert rose: -fx "u" tmp.png
convert: unable to parse expression `'.
-fx does not appear to work in IM 6.4.0-11 Q16-hdri
Re: -fx does not appear to work in IM 6.4.0-11 Q16-hdri
We can reproduce the problem you posted and will have a patch sometime tomorrow.