I have observed that if I insert an ImageInline programmatically into a RichTextBox, like this:
Stream stream = File.OpenRead(
ImageInline image =
then, when I export the XAML of the richTextBox, the Tag attribute is present in the ImageInline tag, as expected.
But if I then enter the Image editor and push the OK button (no actual editing is needed), export the RichTextBox XAML again, the Tag attribute is no longer present and the information originally in it, is lost.
I hope this is a bug and not a feature ;)