shadows are not displayed with CoreText and NSAttributedString

when i try to draw a NSAttributedString with CoreText it won't display the NSShadow attribute.
it will however work when i set the shadow with CoreGraphics before i draw but just not embedded in the attributed string.
am i doing it wrong, or is it just not implemented in CoreText?
CFAttributedString doesn't seem to have a shadow attribute. might that be the problem?
see the code below i use for drawing with CoreText.

best
joerg

Code Block 
NSShadow *shadow = [[NSShadow alloc] init];
shadow.shadowBlurRadius = 10;
shadow.shadowOffset = NSMakeSize(0, 0);
shadow.shadowColor = NSColor.redColor;
NSAttributedString *attrString = [[NSAttributedString alloc] initWithString:@"this is a test" attributes:@{
	NSForegroundColorAttributeName: NSColor.blueColor,
	NSShadowAttributeName: shadow,
}];
 
CTLineRef line = CTLineCreateWithAttributedString((CFAttributedStringRef)attrString);
CTLineDraw(line, currentContext);
CFRelease(line);