Coldfusion exception not caught by containing try/catch - coldfusion

Question

You can run this cftry gist with either the first or second indicated block of code uncommented 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 the struct literal notation {} will sometimes show generically named structs in my debugger, but why should assigning what's created by such syntax make the struct creation happen at a different time than if it's not assigned?
If I debug, I can set a breakpoint on the line where I set temp.userID = 1 and it skips right over it. Moreover, the exception is being thrown on a line contained in a try/catch, but it's failing to catch it.
I know in JavaScript there's the notion of 'hoisting'. I can only assume in some (but not all!) cases CF is doing something similar to struct literals.
Is this a bug, or a known behavior of CF?