1.Open attached "MultipleSelection" Unity project
2.Hold down Control button
3.Select multiple files by clicking on them in the Project tab
4.While still holding Control, right-click and drag selected objects to a different folder

Expected results:
All selected files are moved to a folder
Actual results:
Only the last selected file is moved

Reproduced in: 2017.3.0a2, 2017.2.0b6, 2017.1.0p3, 5.6.3f1, 5.5.4f1

Note #1: While only one file is affected by changes, all files remain and appear selected
Note #2: If you attempt to delete selected files by left-clicking on a file and pressing Delete while Control is held, you receive a prompt to delete all but the last selected file
Note #3: Similar interactions happen when Shift button is held down instead of Control
Note #4: Functions the same way when manipulating selected files in the Project tab or objects in Hierarchy