We've run into a serious issue with CF9 wherein values for certain struct keys can be referenced by other keys, despite those other keys never being set. See the following examples:

Edit: Looks like it isn't just something our servers ate. This is Adobe bug-track ticket 81884: http://cfbugs.adobe.com/cfbugreport/flexbugui/cfbugtracker/main.html#bugId=81884.

<cfset a = { AO = "foo" } />
<cfset b = { AO = "foo", B0 = "bar" } />

<cfoutput>
The following should throw an error. Instead both keys refer to the same value.
<br />Struct a: <cfdump var="#a#" />
<br />a.AO: #a.AO#
<br />a.B0: #a.B0#
<hr />
The following should show a struct with 2 distinct keys and values. Instead it contains a single key, "AO", with a value of "bar".
<br />Struct b: <cfdump var="#b#" />

This is obviously a complete show-stopper for us. I'd be curious to know if anyone has encountered this or can reproduce this in their environment. For us, it happens 100% of the time on Apache/CF9 running on Linux, both RH4 and RH5. We're using the default JRun install on Java 1.6.0_14.

To see the extent of the problem, we ran a quick loop to find other naming sequences that are affected and found hundreds of matches for 2 letter key names. A similar loop found more conflicts in 3 letter names.

<cfoutput>Testing a range of affected key combinations. This found hundreds of cases on our platform. Aborting after 50 here.</cfoutput>
<cfscript>
teststring = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
stringlen = len(teststring);
matchesfound = 0;
matches = "";

for (i1 = 1; i1 <= stringlen; i1++) {
    symbol1 = mid(teststring, i1, 1);
    for (i2 = 1; i2 <= stringlen; i2++) {
        teststruct = structnew();
        symbol2 = mid(teststring, i2, 1);
        symbolwhole = symbol1 & symbol2;
        teststruct[ symbolwhole ] = "a string";

        for (q1 = 1; q1 <= stringlen; q1++) {
            innersymbol1 = mid(teststring, q1, 1);
            for (q2 = 1; q2 <= stringlen; q2++) {
                innersymbol2 = mid(teststring, q2, 1);
                innersymbolwhole = innersymbol1 & innersymbol2;
                if ((i1 != q1 || i2 != q2) && structkeyexists(teststruct, innersymbolwhole)) {
                    // another affected pair of keys!
                    writeoutput ("<br />#symbolwhole# = #innersymbolwhole#");
                    if (matchesfound++ > 50) {
                        // we've seen enough
                        abort;
                    }
                }
            }
        }
    }
}
</cfscript>

And edit again: This doesn't just affect struct keys but names in the variables scope as well. At least the variables scope has the presence of mind to throw an error, "can't load a null":

<cfset test_b0 = "foo" />
<cfset test_ao = "bar" />
<cfoutput>
test_b0: #test_b0#
<br />test_ao: #test_ao#
</cfoutput>