A family of Microsoft word processing software products for creating web, email, and print documents.
There is a text box setting that will produce that magical "Now you see it, now you don't" effect: Placeholder.
Select a textbox in the flow, Right Click (or Control Click) and choose Format Shape. In the left column, click on Layout, then on the Advanced button. In the tab at the top, select Position and make sure Placeholder is not selected. This will deselect the setting for all linked textboxes.
There is also a chance that you may have defined those settings as the default for all new text boxes. If that is the case, right click on a "good" shape and select Set as default textbox.