CF: Unable to perform cfflush in cffunction

OK. This is not an obvious one, so I decided to document this behavior.
Say you have several functions in components processing away happily, and you want to give the user some feedback to keep him/her entertained as well as keep their paws of the back buttons etc..
You think doing couple of flushes during your processing may be a good way until you try and get this error:

Unable to perform cfflush.

You have called cfflush in an invalid location, such as inside a cfquery or cfthread or between a CFML custom tag start and end tag.

What to do? Since none of the hints apply to you. Your code looks like this:

<cffunction name="fFlushIt" hint="flushes current content">
<cfargument name="feedback" default="">

<cfoutput>#Arguments.feedback#</cfoutput>
<cfflush>
</cffunction>

<cffunction name="fProcessing" returntype="numeric"
   hint="does processing" output="No">

<cfset var x=10>
<cfset var y=20>
<cfset fFlushIt("Processing Complete")>

<cfreturn x + y>
</cffunction>

<BR>
<cfoutput>The result is: #fProcessing()#</cfoutput>

here comes the digging into the code and making guesses part. It seems that there is one more scenario cfflush won't like and this is if you call in within a call-tree (yes even nested stuff) in a function that has the output attribute declared as "No". Maybe a hint like that could be placed in the error to avoid all that brain scratching and wondering that goes along with this?
Anyways change the function like this and it worked. Yeah !

<cffunction name="fProcessing" returntype="numeric"
 hint="does processing" output="Yes">

Cheers,