I have a similar problem with my Logitech mouse. If I middle-click my mouse, the Sketchup (v15.1.106 x64) cursor changes to the orbit tool for a fraction of a second, but then immediately switches back to whatever tool I was previously using. However, I am (intentionally) using the default Microsoft mouse driver in Windows 8.1, so my computer has no option to reassign the middle mouse button. The mouse works fine in all other programs, where clicking my mouse wheel is correctly interpreted as a middle mouse click.
How do I get this to work with Sketchup so that a middle click will temporarily change to the orbit tool?