Repro steps:
1. Open attached project
2. Select the Hand Tool in the Toolbar
3. Position the cursor at the top of the Scene View
4. Hold Alt, and right-click and drag up to zoom out the Scene View until the Camera is under the Grid placing the cursor beyond the top and to the bottom of the screen
5. Zoom in until the Camera is over the Grid and the cursor is back at the top of the screen
6. Repeat steps 4 and 5 rapidly

Expected: After continuous zooming in and out and placing the cursor to the initial position the Camera is also in the initial position
Actual: After continuous zooming in and out placing the cursor at the initial position seems to have moved the Camera under the Grid

Reproducible with: 2017.4.9f1, 2018.1.9f1, 2018.2.4f1, 2018.3.0a8