When you add a caption to a "floating" object (that is, to an object whose Text Wrapping is something other than "In line with text"), Word always places the caption in a text box.

I can't explain why the text boxes end up in the wrong places, though. Does this happen in a specific document, or can you reproduce the problem in any document?

Note that you could place objects "In line with text" and then add the captions as ordinary paragraphs in the main body of the text. If you need to wrap text around object plus caption, you can use the Insert Frame command, which you can add to the Quick Access Toolbar. (In the Quick Access Toolbar category of File | Options, look for the Insert Horizontal Frame command.)

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional