I'm seeing it on an Intel Macbook (1st Gen), 10.5.2, Word 12.1.0.
After more investigation, I can only reproduce in one document. See
below for more.
It's a 27 page document, no tracked changes, some comments, an
embedded ToC, lost of autonumbered headings, some footnotes.
One document, doesn't seem to matter where, but the selection does
need to straddle a page boundary.
Nothing happens - Word just locks up.
Hope the above info helps. Anything else I can try?