I would agree that this feature can be annoying (if you find yourself screaming at your computer "
STOP CHANGING THINGS!" you know a
design feature is bad..).
However in its defence (watch the downvotes roll in) you can alter the arbitrary choices it makes on your behalf. If you can be bothered to mess around in the guts of the tabbed menu system, you have the power to add or delete grammar decisions.
What does this mean? Why you can make up your own grammar rules, add them in and make word completely unusable for anyone else. Of course, your writing would also be unreadable but it might be fun on a rainy afternoon...