[grammatim[_2_]]

I'm using complicated Equation fields to create linguistics
expressions. Usually there is no problem with arrays nested inside
braces or brackets inside other braces, but every so often, an Array
(an \A entry) will not stay within the pair of braces, or to the right
of a left-brace. Instead, the last line, or several lines, shoots to
the left and overprints whatever is on the line before the brace; and
there's also a big space to the right of the lines before the closing
right-brace.

This happens both with some items that were created in MacWord2001 a
few years ago and transferred to a Word2007 .docx file, and with some
newly typed items. It _might_ be more common with long lines in the
array, and it might be less common when there are other braces nested
within the multi-line arrays.

I can find nothing that all the culprits have in common.

The field syntax is correct; if it isn't, Error! appears when field
codes are toggled. (The most common source of error is Word's
insistence on matching a closing fence; since you tell it to use
braces or brackets instead of parentheses by typing \{ or \[ before
the matter to be enclosed, Word wants the closing parenthesis of the
field scope marker to be a } not a ) so you have to remember to undo
the change.)