<up> or <left> clearing the mark in Emacs 23.2

[John McCabe]

I've only recently moved to Emacs 23.2 from 22.3, and I'm finding
something a bit odd and not sure where to look for details. It may be
something to do with my settings, and I'll upload my .emacs etc if
necessary, but I was hoping someone might just know the answer off the
top of their head.

On 22.3, with transient-mark-mode enabled, if I have a buffer of text,
go to the start using C-Home (beginning-of-buffer), set the mark
(C-@), go to the end of the buffer using C-S-End (end-of-buffer), then
go up a line using the up arrow (previous-line) or left arrow
(backward-char) then the highlighted region changes to between the
mark and the point as I think has been the case for many years.

On my 23.2 setup, which uses basically the same .emacs and other
initialisation files (so may have some obsolete configuration settings
still in there - don't know how to tell if these have changed meaning
or are really obsolete), when I do the above sequence of keypresses,
the highlighted region disappears when I press the up or left arrow.

Something seems to be clearing the mark when I do this.

If anyone can suggest why this is I'd really appreciate your help.

Thsnks

John