Text objects do not update if Text Fields are empty

I use text fields in annotation objects on page layouts. If the user text which i use in an annotation object contains text, everything works fine. As soon as i clear the text (or enter spaces) the annotation object either does not update anymore or will show the formula in the annotation object like in the screenshot:

Attached you find the 3dm file:

text_issue.3dm (88.0 KB)

Any ideas how to fix this?