I'm not sure this is a bug or a feature, but the behaviour is bizarre,
IMHO and at the very least I'd like to turn it off. It happens in
whenever auto-fill-mode is on and even in the vanilla Aquamacs
without customizations. It happens when the frame is not much wider
than the
value of 'fill-column'. It is difficult to describe in words, but I
will try my best.
Consider a paragraph of text consisting of several (>3, say) lines,
whose lines have been wrapped. For example, take the above paragraph
starting this email. Suppose I put the cursor at the end of the third
line (after 'Aquamacs without'), I type a space and C-d. The line
gets wrapped and the ... appears on the margin. So far, so good. If
I now do a C-e, the cursor does not move to the end of the line (which
would be at the end of 'than the') but rather stops between the 'u'
and 's' of 'customization'. Is this intentional? If so, why? and,
more importantly, how do I reinstate the old behaviour?