NSAttributedString drawRect doesn't draw images on-screen on Mojave

Question

I have a working app that draws NSAttributedStrings into a custom view. The NSAttributedStrings can included embedded images. This works on versions of macOS prior to Mojave. The app can display the strings on screen, print them, and save them to image files.

This is apparently broken under Mojave. Weirdly, printing and saving to image files still works; but on-screen, the strings display only the text and not the embedded images. Proper space is left for the images, but that space is blank.

I've tested by building a small app that shows a window with an NSTextField (a label) and a custom view. It makes a single NSAttributedString with an embedded image. It applies that string to the attributedStringValue of the label, and also calls drawInRect: on the same string in the drawRect: method of the custom view. In the label, the string is displayed correctly, image and all. But in the custom view, only the text appears, and the space where the image should be is blank.

Anybody got a clue why this is happening on Mojave but not on earlier versions of macOS?

Here is the code that makes the string (and caches it, for re-use):

static NSMutableAttributedString* sgAttrString = nil;

/*
 * Creates an attributed string the first time it's called,
 * then returns that same string each time it's called.
 */
+ (NSAttributedString*)getAttributedString
{
    if (sgAttrString == nil)
    {
        NSFont* font = [NSFont fontWithName:@"Helvetica" size:24.0];
        NSDictionary *attrs = @{
                                NSFontAttributeName: font
                                };
        sgAttrString = [[NSMutableAttributedString alloc] initWithString:@"Daisy: " attributes:attrs];
        NSImage* daisy = [NSImage imageNamed:@"daisy.png"];
        [daisy setSize:NSMakeSize(24,24)];
        NSTextAttachment *attachment = [[NSTextAttachment alloc] init];
        // I'm aware that attachment.image is available only on macOS 10.11 and later.
        // It's not an issue in my real project.
        attachment.image = daisy;
        NSMutableAttributedString* imageStr = [[NSMutableAttributedString alloc] init];
        [imageStr setAttributedString:[NSAttributedString attributedStringWithAttachment:attachment]];
        [sgAttrString appendAttributedString:imageStr];
        [sgAttrString appendAttributedString: [[NSAttributedString alloc] initWithString:@" !!" attributes:attrs]];
    }

    return sgAttrString;
}

Here is the code that applies the string to the NSTextField:

NSAttributedString* str = [Utilities getAttributedString];
self.label.attributedStringValue = str;

And here is the code that draws the string in a custom NSView:

NSAttributedString* str = [Utilities getAttributedString];
[str drawInRect:NSMakeRect(50,50, 300, 40)];

Again, this behavior seems to occur only in Mojave! Thanks in advance for any help.