Ok – now resolved!
Under Prefs > File Handling, ‘Check links before opening document’ needs to be selected.
‘Find missing links before opening…’ can be on or off.
You need to restart InDesign for the preference change to take effect.
* It didn’t matter that all links were already perfectly linked in both documents. *
It seems that if InD doesn’t ‘check links’ it will break them and you’ll be left with a preview of all raster content in the embedded InDesign file (text/vector content remains text/vectors). This bug does occur in CS6 too (when ‘check links’ is off in prefs).
You need to accept a longer file opening time in order to get usable output when working with placed InDesign files that contain raster content. For all other occasions, you can keep ‘check links’ off and have a quicker file opening time.
