"enter" key in Mac Mail erratic (in preview pane)

Question

Hi,
I finally moved from Snow Leopard to Yosemite.
I noticed that the behavior of the 'enter' key (the misnamed key that should be called 'return', #1)
when used in the message preview pane is erratic.
Hitting 'enter' always deletes the highlight message ... that's expected.
But what isn't expected is that sometimes the highlight moves *down* to the
next older message, and sometimes it moves *up* to the next newer message.
The behavior I've seen for the last four "enter"s: down, up, up, down.
This is highly disconcerting, and I've already lost (into the trash) emails due to this ...
because as I'm hitting "enter" to delete the current message, I've reading ahead,
I see the message above (where I expect the highlight to go), and have decided
"yeah, I'll delete that too" ... and I hit the enter key a second time, before realizing
the darn highlight moved the wrong way.
I've done a fair amount of testing ... including:
   - having the above message being read vs. not yet read
  - having the below message being read vs. not yet read
  - using arrow/mouse to move to a mesage
There's no apparent cause/effect.  About 80% of the time, 'enter' deletes and
then moves up ... 20% of the time it deletes and moves down.
As you may guess, Snow Leopard's Mac Mail *always* moved up for me
View:
  [x] sort by date (and, clicked on date so newest is at top, not bottom)
  [x] newest message on top
(nothing else checked; I've previously clicked on "Expand all conversations",
but rather than showing it checked, sigh, it's now grayed out (along with
"Collapse all conversations", and "Organize by conversation" is black (not grayed
out, and not checkmark).
Prefs:
  General:
      mail .app / Auto / None / [x] play / inbox only / inbox only / never /
      Downloads / After Message is Deleted / Show a list,
      three checkboxes are unchecked
     (i.e., nothing having to do with viewing
   Viewing
     [x] Use classic layout
      List Preview [2 lines]   (note: I suspect this should be grayed out
     when "classic layout" is selected, since (a) it has no effect, and (b)
     classic view uses a single line per message.)
     [x] load remote content
     [x] use smart addresses
     all else unchecked
   The other Prefs categories (Accounts, Junk Mail, Fonts & Colors,
   Composing, Signatures, Rules, Mail Hub) have no apparent
  controls that seem related to this.
I do have MailHub installed, but I'm not aware of it having a potential
to affect this behavior.
thanks,
Stan
#1. I mentioned "enter" vs. "return" to clarify that I mean the "normal" key people
nowadays think of as "enter" ... not the "keypad enter" (the "enter" key on
the numeric keypad / secondary keypad).  I'm just being pedantic, I guess : )
Message was edited by: sieler
(fixed minor typo)

Answer 1

Er, make that "backspace", not "enter", to delete the highlighted message.  Sigh, sorry!
However, I found the answer.
Assume you've hit the up or down arrow in the message preview pane.
Now, "backspace" will delete the highlighted message *and* move in the
same direction as your last up or down arrow! 
In effect, Mail says "hmm...you were moving in direction X before, so you probably
want to move in direction X again". 
(Had there been no up/down keypress since starting Mail, "up" is the default direction.)
And if your last direction was indicated by pressing pageUp or pageDown?
...trick question ... those don't move you in the message preview pane
Annoying, but at least I (think) I understand it.
Stan