this used to be merely annoying, but now it's eating text as I write it
(i hadn't been doing much editing before).  Anywhere from one to four
lines up from the present cursor position (ie, to the left of the cursor
on the present line, to directly above it).  This highlights, and, in an
editor, almost anything, including left-button, deletes it.  

My hands are nowhere near the mouse when this happens.  It seems to
happen (sometimes) with space.  My left hand is up to high to make
contact, although there is a possiblity that i'm brushing command, option,
(jut happened, *)&(^(*, though i was in emacs, noot lyx, so it went up a
few lines instead--emacs defies regular text selection) or possibly even
control.  But try as i may, i can't reproduce it.

The mouse is a kensignton turbomouse, and there's an apple mouse
connected too.

does anyone have any clue what this is?

rick