Yes, Word does this on purpose. Whenever you insert a TC, TA, or XE field,
since they are all formatted as Hidden text, Word displays nonprinting
characters, which include Hidden text. Otherwise, you would not be able to
see what you were doing. If you find the other nonprinting characters
distracting, you may find it helpful to check the box for Hidden text (and
deselect the box for All) on the View tab of Tools | Options. Just be aware
that when you have done this, the Show/Hide ¶ button will toggle between
display of Hidden text only and all nonprinting characters (there won't be
any way to toggle off the display of Hidden text).
Since I ordinarily work with all nonprinting characters displayed (but find
the display of Hidden text distracting, and need to be able to toggle it off
for generating the TOC/Index), I usually do this the other way
around--toggling between display of all nonprinting characters and display
of all but Hidden text, though of course Word does toggle that back on every
time I insert an XE or TC field.
