An odd occurrence.
Checking out some configuration ideas, I opened Explorer Panel Settings and, in the Save on Exit section unchecked the Remember open paths option.
The odd effect is that, in the right hand pane both the folder tree and file view window were behaving as expected but, in the left hand pane, whilst the folder tree was fully functional, the file view window was blank. The only way I could repopulate it and return the the original settings, that is, with the Remember open paths option checked, was to restart the computer.
No real harm done, other than the inconvenience but this seems odd behaviour. Even more irritating was the fact that there seemed to be no obvious way to repopulate the pane; using soft or hard refreshes had no effect.
Minor bug, or operator error?