1. Create new project and add new C# script, make sure that layout is reset to Default
2. Open said script in MonoDevelop and switch back to Unity. DO NOT minimize MonoDevelop, only switch (location or size of MonoDevelop window does not seem to matter)
3. Press Win+D twice - to minimize and bring back up all the windows
4. Notice that after bringing it up, the inspector window is dragged all the way to the left

Tested on Win10
Reproducible in:
5.0.3f2, 5.1.4f1, 5.2.0p1, 5.2.1p4, 5.2.2p3, 5.3.0b5

Bug in action: http://screencast.com/t/keBG5iqAGLLJ