Why does sysopen not assign the fd param in this case?

[Marlon Richert <marlon.richert@xxxxxxxxx>]

Why doesn't sysopen assign the fd parameter during startup, yet it
does assign it correctly on the command line afterwards?

% cd $(mktemp -d)
% > .zshrc <<EOF
zmodload -F zsh/system b:sysopen
PS1='%# '
PS4=+
set -x
sysopen -r -o cloexec -u fd <( sleep 1 )
print fd=$fd
EOF
% env -i HOME=$PWD PATH=$PATH TERM=$TERM ${TERMINFO:+TERMINFO=$TERMINFO} zsh -d
+sysopen -r -o cloexec -u fd /dev/fd/12
+print 'fd='
fd=
+sleep 1
% sysopen -r -o cloexec -u fd <( sleep 1 ); print fd=$fd
+sysopen -r -o cloexec -u fd /dev/fd/11
+print 'fd=15'
fd=15
% +sleep 1