Superscript key-command inconsistency

[M. Katz]

I'm trying to write the mathematical symbol for ArcSin, as sin to the
-1 power. This should be a no-brainer, but Word mangles this simple
task in its charming way.

Try this. On a new line, type "sin" then hit the command keys for
superscript (that's command-shift-+ for me, or just command+ if you
prefer.) Now you can type "-1" and it's all fine.

But suppose you already had "sinx" on the screen. Place the cursor
between the n and the x and hit command+, the whole word "sinx"
becomes superscripted. The formatting I'm trying to apply _after_ the
insertion point goes ahead and mangles the characters before the
insertion point. Even better, suppose you have sinx/z and you want to
insert a -1 superscript between the n and the x, as before. Now when
you try it, the sinx becomes superscripted, but the /z does not.
Parantheses can also stop the superscript from propagating.

I notice that this also happens for bold. If the cursor is "in" a
word, the whole word becomes bold. If the cursor is at the end of the
word, the bold starts at the cursor.

Can we turn this feature off somehow?

M. Katz