Steven,
I've been there too.
1) upgrade -- 2.24.x is fixed
or (I'm assuming you're in the in-box with view selected as unread)
2) use v-folder (search folder) with folder view = 'view all'.
Search filter is "all unread"
or
3) turn off "mark as read after N seconds" in mail pref's. , & use
Ctl-
When I double click on a single message (not using message preview) the
mail viewer opens, I see the message for a second and then the display
is a blank message / page.
If I go back and use the preview message (Ctrl-M) function I get the
split screen and can see the message fine. Can you tell me
