Since Nisus does not allow columns (right?), I am trying to put small notes in the margin by placing a number of floating text boxes (Floating Shape > Text Box).
I blurred the text because it doesn't matter. As you can see, there are three floating text boxes in the right margin. But the top two are not responding! I cannot select them, let alone edit (or delete).

They also show up when I render a PDF of the document:

But sometimes, when I scroll a bit in my document, they disappear:

Please help! I need to edit them, or at least be able to delete them!
Is there a different solution I could go for, to have little comments in the margin?