Odd Difference Between Windows Git and Standard Git

I'm running Git version 2.8.2 built from source on Ubuntu 16.04. I'm using a repository that's stored on Dropbox. I'm the only person accessing this repo. Everything works great.

For reasons unrelated to Git, I decided to try Git for Windows, so I installed "git version 2.8.2.windows.1" on Windows 10. When I run 'git status' on Ubuntu the list I see is exactly what I expect. However, when I run 'git status' on the same Dropbox repo on Windows, I see what I expect plus I'm told that every .pdf file and some .png files are modified.

I'm guessing that this is caused by some mishandling of binary files. Is this behavior to be expected? If so, is there something I can do to have the output on Windows be the same as on Ubuntu? I'm aware of 'git update-index --assume-unchanged' but this seems harsh.

I copied the repo to a non-Dropbox location, just in case it was Dropbox that was causing the problem, but this didn't make any difference.

(If you want to try this yourself, try it on the ProGit2 book source on Github).

Thanks, Jon Forrest