Substring expansion "${string%%' '*}" doesn't work

[janlz]

The following substring expansion to get the first word of a string separated by spaces doesn't work using dash 0.5.8-2.10 on Ubuntu 18.04 LTS:

string="one two three four"
first="${string%%' '*}"
printf "%s\n" "$first"

It prints "one two three four", instead of "one". This works on bash and Solaris sh, but not in dash.

Oddly, not putting the white space between single quotes works:
string="one two three four"
first="${string%% *}"
printf "%s\n" "$first" # Prints "one"