Can not use relative path in build directory

I can't  use relative path in build directory. I don't know if this is a bug or designed like this.But at least the cursor works strangely

• I tap backspace to clear build directory, 
• When I want to delete the last letter, the build directory completes my path and adds the drive letter'D '
• I finally clear build directory
• When I enter the first letter 'b' of "build" in the empty path, the build directory automatically fills in the absolute path and moves the cursor after the first letter