First, you need to use & instead of $amp; (turn off the rich text editor -- it’s translating the ampersands).
Also, I think you need &thumb_use_dropshadow=`1` and maybe &thumb_use_imagemask=`1` in your snippet call. You’ll need to re-upload the images.
This is kind of a wild guess, but did you clear the MODx cache and your browser cache before uploading? You might have uploaded through an older version of the page.
I just cleared both, same result.
Hmm.. so which call you are using to upload the pictures?
If you have those calls in a single document, you shouldn’t be able to even upload pictures through picture management, as it would show the management from both documents and mess things up. You should be using another document for the uploading, Eg. have all the picture size and shadow etc parameters there with &is_target=`1` and use &manage_target parameter those above calls to redirect the picture management to that separate document.
"He can have a lollipop any time he wants to. That's what it means to be a programmer."
FWIW,
Applying
http://modxcms.com/forums/index.php/topic,21619.msg134052.html#msg134052
and changing all chmods 0666->0644 | 0777->0755 in MG php-files and galleries folders/pics on ftp-server,
helped me running multiple calls (+hiding managment with @CODE:) and still upload through the same document.