Cant use vertex snapping square handle when in some basic isometric views. Specifically Top, Right and Left views.

To reproduce:

1. Open "New Unity Project 1" with Unity 5.4.0f3;
2. Open main scene;
3. Enter Isometric view.
4. Select "Cube" game object/
5. Try to use vertex snapping while in different basic views (top, front, right, left, back). Aim for the sphere.

Results: Snapping works as expected.

6. Now do theses same 1-5 steps with "New Unity Project 2" using Unity 5.5.0p1.

Results: Cant snap while in Top view, sometimes cube jumps to very high or very low Y coordinates.
Cant snap while in Right view, sometimes cube jumps to very high or very low X coordinates.
Cant snap while in Left view, sometimes cube jumps to very high or very low Z coordinates.

Reproduces with 5.5.0f2; 5.5.0f3; 5.5.0p1; 5.6.0b1;
Doesn't reproduce with 5.4.0f3;

Note: Both example projects are attached to this letter.