[scribus] Disappearing frame

[Hicks Tim]

Scribus newbie here, be kind. 

I prepared a multipage document. When it was ready I exported to PDF. 
Pre-flight inspector reported no relevant problems. 
But one of my text frames vanished from the PDF.
There seemed to be nothing unusual about it. 
 
In the end I had to copy the contents, delete the frame, create a new frame, and paste the contents back. 
The new frame exported as expected. 

Has anyone seen this? Is there an explanation?
If I have to shrug and just write this off, it wouldn't be the first time I've done it with page-layout software. 

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Tim Hicks, Victoria, B.C. Canada