Expansion of ${!x*} and ${!x@}

[Linda Walsh]

The manpages for "my" bash's (3.1.11 on Linux and 3.1.17 on cygwin/i686),
under Parameter Expansion, say:


    ${!prefix*}
    ${!prefix@}
       Expands to the names of variables whose names begin with prefix,
       separated by the first character of the IFS special variable.

---
From this, I'd expect both forms to have the same output.
Is this what is intended and what I should expect?

For test purposes, I set:
  IFS="<" OFS=">"   # (also set "Output" FS to see if it is used
                    #  in the output of 'echo')
---
I used 4 tests, all with prefix=U, 1st pair unquoted, 2nd pair quoted.
input:
  echo ' * ' =  ${!U*}    ; \     # (line 1 - * unquoted)
  echo ' @ ' =  ${!U@}    ; \     # (line 2 - @ unquoted)
  echo '"*"' = "${!U*}"   ; \     # (line 3 - * quoted)
  echo '"@"' = "${!U@}"           # (line 4 - @ quoted)
---
output:
   *  = UID USER                  # (line 1)
   @  = UID USER                  # (line 2)
  "*" = UID<USER                  # (line 3)
  "@" = UID USER                  # (line 4)
---

QUESTIONS continued...
- If the two forms are supposed to be identical, why aren't lines
  3 & 4 the same?
- Why do the quotes in line 3 make for different output than in line
Why aren't the 4 lines identical?  I see the IFS, "<" in line 3, but
not in lines 1,2&4.  Why isn't it in all 4 lines and, also, even
the double quotes make a difference when expanding variables, why
aren't lines 3&4 the same?