Reproduction steps:

1. Create a New Project
2. Single or multi-touch any window
3. Multi-touch the same window at a different location

Expected Result: Only the circles, indicating a touch point, should appear
Actual Result: A white box appears on the first touch point of a multi-touch/ A white box appears on the last touch point when multi-touching

Reproduced with: 2018.2.0b2, 2018.1.0f2, 2017.4.2f2, 2017.3.2f1, 2017.2.2p2, 2017.1.3p3

Note:
Reproduces in the Editor and the Player

Every window is separate, e.g. touching the Console window and then multi-touching any other window will not reproduce the issue, but if after that you then multi-touch the Console window, it will reproduce

Only reproduces on touchscreen devices
Tested on a Microsoft Surface Pro 2