Reproduction steps:
1. Open the attached project (or any project)
2. Go to Edit->Preferences->External tools
3. Make sure your script editor is not Monodevelop (tested with VS2015)
4. Uncheck "editor attaching"
5. Restart the editor
6. Go to Edit->Preferences->External tools

Expected result: "editor attaching" field is NOT checked, as the editor is not attached to the debugger now
Result: "editor attaching" field is checked

Reproducible on: 5.4.4p1, 5.5.1p2, 5.6.0b7, 5.6.0b11, 2017.1.0a2
Not reproducible if Monodevelop is selected as script editor (only tested with it and VS2015)

Tested on Windows 10