Thread:Project:Support desk/ImageMagick Thumbnail error: "no decode delegate"; "no data returned"/reply

I'm able to reproduce the error from the command line, though I'm still trying to understand it. Here's the invocation coming from MediaWiki:

convert -quality 80 -background white -size 120 /Library/WebServer/Documents/mediawiki-test/images/b/b0/Dan4.jpg -thumbnail 120x120! -set comment File source: http://[wiki URL]/index.php/File:Dan4.jpg -depth 8 -sharpen 0x0.4 /Library/WebServer/Documents/mediawiki-test/images/thumb/b/b0/Dan4.jpg/120px-Dan4.jpg

Running this from the command line produces:

convert: no decode delegate for this image format `' @ error/constitute.c/ReadImage/532. convert: no decode delegate for this image format `/var/tmp/magick-V5ijtHg1' @ error/constitute.c/ReadImage/532. convert: no data returned `http://[wiki URL]/index.php/File:Dan4.jpg' @ error/url.c/ReadURLImage/231.

If I replace the "-set comment ..." option with "-set comment xxx", it runs successfully:

sudo convert -quality 80 -background white -size 120 /Library/WebServer/Documents/mediawiki-test/images/b/b0/Dan4.jpg -thumbnail 120x120! -set comment xxx -depth 8 -sharpen 0x0.4 /Library/WebServer/Documents/mediawiki-test/images/thumb/b/b0/Dan4.jpg/120px-Dan4.jpg

It appears the thumbnail command is being interpreted as a request to load an image from the given URL.

Is this just a bug? Why is nobody else experiencing this?