I didn't explain this well enough.
When dragging the text boxes, they will disappear completely. No handles, no invisible box, no nothing. When you stop dragging, there is nothing there. The text box has gone to meet its maker in text box heaven.
I've noticed some other peculiarities. When constrained with the shift key to purely vertical or horizontal movements, the text is visible and will survive. When dragged to a random position...poof!
And as mentioned in the previous post, this doesn't happen in every project, or even in all views within the same project. My current work-around: plop a hotspot at the desired text block location, the the dragged text block will re-appear when the hotspot is touched.
From an existential point of view, one has to wonder where those disappearing text blocks have gone...