Microsoft is continually making a lot of changes in W-10 to make 4K screens display properly. Many changes were just made in October to accommodate two monitors, where one is a 4k. However, the articles and blogs by the developers at MS can't possibly make all the changes required in everyone's software. I have a 4k screen set at my recommended 250%, and most everything works and looks great. But some programs must also be changed or they will never look OK.
Make sure you also play with this control: (Control panel: Customize your Display: "Change the size of text, apps, and other items: 250% recommended")
Read and follow the following Windows.com developer blog:
October 24, 2016 - High DPI Scaling Improvements for Desktop Applications and “Mixed Mode” DPI Scaling in the Windows 10 Anniversary Update