mouse-face hightlighting fails with inserted unicode

[Stephen Berman]

With Emacs 22.1, 23.0.50 and 23.0.60:

1. emacs -Q
2. Type some characters, e.g. "aa".
3. M-: (put-text-property (point-min) (point-max) 'mouse-face 'highlight)
4. Run the mouse over "aa" and see the highlighting over each character.
5. Type another character; now the buffer displays e.g. "aba", and still
all characters show mouse-face highlighting.
6. Delete the "b" and type M-: (insert (format "%s" "\x62"))
   => Now the buffer again displays "aba", but "b" does not show
   mouse-face highlighting.
7. Delete the "b" and type M-x ucs-insert RET 62 RET
   => Again the buffer again displays "aba" and "b" does not show
   mouse-face highlighting.