How to reproduce:
1. Open the attached "1287927 repro" project
2. Open the Input Debug window from Window > Analysis > Input Debugger
3. Click on the Options dropdown menu in the Input Debug window
4. Enable Simulate Touch Input From Mouse or Pen
5. Open the "SampleScene" Scene from the Assets > Scenes folder
6. Enter Play Mode
7. Click on the red rectangle in the Game window
8. Open the Console windows from Window > General > Console

Expected results: 1 message "t" is logged
Actual results: 2 or 3 messages "t" are logged depending if the mouse was moved while clicking or not

Reprocudible with: 1.0.0-preview.7 (2020.2.0b2), 1.0.0-preview.9 (2020.1.11f1, 2020.2.0b2)
Could not test with: 2018.4.28f1, 2019.4.14f1 (UI Toolkit not available), 2020.2.0b3, and newer (UI Toolkit doesn't compile)

Notes:
-This seems to be happening because the "Click" Action of the "UIToolkitInputActions" Asset (included with the UI Toolkit package) is triggering the PointerDownEvent from the Mouse Binding as well as from the Touchscreen Binding
-Moving the mouse while the left mouse button is still pressed will print one additional message