I did a little troubleshooting on my setup. I have the same version of Office as you do. I have traced the problem as well. It happens if you enable UI Automation for Microsoft Word. With it turned on:
1. Create a table with more than 2 columns.
2. Type "dog" in the first column.
3. Press Tab to move to the next column
3. Type "cat" in the second column.
4. Press Shift+Tab to move to the previous column.
NVDA will say: "Column 1, Dog", as it should, but then it will add the following: "Dog selected, cat unselected". I hope you can understand the issue.
My advice? Turn off UI Automation in Word, or perhaps create a profile NVDA+Control+P, then turn ooff the setting, then bring up the configuration profile dialog when you need to use tables. You can even set a shortcut to the profile in the Input gestures dialog.
That's for now though, as it needs fixing.