You may be bringing a Table to its limits. Word can and does handle much larger an more complex documents.

First, are you using Styles exclusively for formatting your text?
Second, you could use text boxes in the margin for your tab notes. These can be anchored to the text and need not have any border. This might do away with the need for the tables altogether. It would make your document much more manageable.
Third, why can you not end a table and start a new one? If you have tables going on and on, it stretches the construct. I am guessing you have tables spanning more than ten pages that simply hold text.

and, from my last post... Do you have track changes turned on?