Coldfusion exception not hitting try / catch list

You can run this cftry gist with the first or second block of code specified, without comment, to see the problem.

<cffunction name="alpha" returntype="boolean">
    <cfargument name="boo" type="boolean" />
    <cfreturn arguments.boo />
</cffunction>

<cffunction name="beta">
    <cfset var temp = {} />
    <cftry>
        <cfset temp.userID = 1 />

        <!--- This way throws an *unhandled* exception --->
        <!--- --->
        <cfif alpha(structAppend({userID = temp.userID}, foo))>
            <cfdump var="It worked" />
        </cfif>


        <!--- This way works as expected --->
        <!--- 
        <cfset temp.args = {userID = temp.userID} />
        <cfif alpha(structAppend(temp.args, foo))>
            <cfdump var="It worked" />
        </cfif>
        --->

        <cfcatch>
            <cfdump var="#cfcatch.message#" />
        </cfcatch>
    </cftry>
</cffunction>

      

        
        
        
      

    

I know that string literary notation {}

sometimes displays the common names of structs in my debugger, but why should I assign something created with this syntax so that the creation of the structure happens at a different time than if it wasn't assigned?

If I am debugging, I can set a breakpoint on the line where I set temp.userID = 1

it and it jumps right over it. Also, an exception is thrown on the line contained in the try / catch, but fails to catch it.

I know JavaScript has the concept of "hoisting". I can only guess in some (but not all!) Cases where CF does something similar to string literals.

Is this a bug or a known CF behavior?