[MlMt] Read next message using space?

[William P. N. Smith]

I keep getting the tip that I only need the space bar to read the next 
message, but that doesn’t work, and to read the last message in a 
thread I have to manually expand the thread and select the message to 
read with the Return/Enter key.

Is it possible I have a setting wrong?  I can’t find anything 
applicable in Preferences…

Thanks!