shell prefix/suffix removal with quoted word

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

It has been brought to my attention that quoting the "word" in sh's 
substring processing causes word to be matched literally rather than 
being treated as a pattern. I.e.,
	x="abc"
	y="?"
	echo "${x#"$y"}"
outputs "abc", while
	x="abc"
	y="?"
	echo "${x#$y}"
outputs "bc".

I can't see this behaviour specified by SUS nor mentioned in sh(1).
bash and ksh seem to behave the same.