Uncontrolled text selections

This occurs in Outlook and Word 2002 SP3:

When I select text using the shift key and the direction-
arrows or a mouse-click, whether two characters, two
words, or two paragraphs, and I continue hold the shift
key down for a couple of seconds, while I decide whether
to include a bit more in the selection,one of the
following occurs:

1) some portion of text FOLLOWING my selection, maybe two
and a half additional paragraphs, perhaps including the
first couple of characters of a word, are suddenly
highlighted and included in my selection

OR

2) some portion of text PRECEDING my selection, maybe two
and a half additional paragraphs, perhaps including the
last couple of characters of a word, are suddenly
highlighted and included in my selection

OR

3) some portion of text, maybe one and a half words, loose
their highlighting and are dropped from my selection.

To try to fix the situation:

Sometimes, when I release the shift key, and press
the "ESC" key, the selection does not become unselected.

Sometimes clicking the mouse also does not de-select it.

I just have to wait for it to get ready to behave.

Or, I click Ctrl-Alt-Delete/Task Manager, all programs
indicate "running." I hit ESC, returning me to the
document, which now shows no selection, and I start over.
It ususally behaves normally for a time.

NOTE: Selecting by click-and-drag has a different problem:
the selection sometimes just goes into an uncontrolled
scrolling behavior - continuing up or down uncontrollably,
all the way to the end of the document. I do not have
scrolling selected (start/settings/control panel/mouse)