[racket] does #:scale work in @image?

According to the docs [1], Scribble's @image command takes a #:scale parameter like so:

> #lang scribble/manual
> 
> @image["foo.gif" #:scale 0.4]

However, though the 'scale' argument appears in the 'doc exported by the Scribble file, regardless of how I set #:scale, the generated HTML looks like this:

> <img src="foo.gif" alt=""/>


So it appears 'scale' is getting dropped during the HTML render ... or is there a wrinkle I'm overlooking? 



[1] http://docs.racket-lang.org/scribble/base.html#%28def._%28%28lib._scribble%2Fbase..rkt%29._image%29%29
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