A better, more flexible, way to work with text shadow is to render the shadow on a new layer. This method will allow you to manipulate the shadow-text, as needed, without affecting the background. Finally draw the actual text on top of the shadow after adjusting any geometric offsetting. Here's an example:
convert -size 280x100 pattern:SMALLFISHSCALES \
\( xc:transparent -font "Menlo" -pointsize 32 -fill black -draw "rotate -4 text 20,60 'ImageMagick'" -blur 0x1 \) \
-geometry +2+2 -composite \
-font "Menlo" -fill white -pointsize 32 -draw "rotate -4 text 20,60 'ImageMagick'" \
example.png
The escaped braces "\( \)
" will create a new sub-image; which, will be applied to the background with -composite
flag.
This solution is a little bit more labor intensive, but keeps all your effects isolated.