Think i found a bug hopefully.
1-Product and version - FM16 advanced 16.0.3
2-OS and version - macOS 10.12.6
3-Browser and version - N/A
4-Hardware - ?
5-Description - When i click "New Window" in top menu bar under window and duplicate my current window. I can only close the original window, i cant close the newly duplicated window. (IE.. Original window name = "MyWindow" and newly duplicated = "MyWindow - 2". "MyWindow - 2" CAN NOT be closed. only "MyWindow" can be closed. Also when that happens in the new window if i click in a field then i cant see the cursor and cant see that im in the field but if i resize the window just a tad then all the sudden i can see my cursor but it continues till i close filemaker and reopen.
6-How to replicate - Clicking New Window under Window main menu
7-Workaround - Close filemaker completely to get it back.