Why is that a problem?

The meaning of 

/a/b/<c/>

is that for every b under an a, a new c is created. E.g., it is the same as

for $i in /a/b return <c/>

ok. But that means selection and return control are in one statement.
What would then mean /a/b/<c/>/d/e 

(In reply to comment #2)
> ok. But that means selection and return control are in one statement.
> What would then mean /a/b/<c/>/d/e 
> 

it selects nothing as <c/> has no d children but
/a/b/<c><d><e/></d></c>/d/e 
would select one (newly created) e node for each /a/b node selected from the
original context.
It looks odd, but just think of each step as being a function returning some
sequence of nodes, and think of <c>....</c> as being a function that returns a
sequence of one new node, and it all works out in the end.

This does not seem to be comment on Formal Semantics proper, but on XQuery 1.0
semantics in general.

XQuery 1.0 allows arbitrary expressions on the each side of the '/', the
semantics is well defined, although sometimes odd for certain cases.

- Jerome

Dear Wim

The WG took a look at your questions and thinks that Michael's and David's 
answers provide you with the correct explanations. Since it does not lead to a 
change in the specifications, we will mark it as invalid.

If you agree with our resolution, please mark the bug as closed. 
If you disagree, please reopen.

Thanks
Michael (speaking for the WG)