System Information
Operating system: Windows 10
Graphics card: GTX 960

Blender Version
Broken: 2.80, e1b5fe156db2, 2019-02-05

Short description of error
note: described using left slick select, but occurs when using right click select as well

• User action: Left click on a blank area in the UV editor viewport, either in select or transform mode
• Resulting behavior: The nearest vertex/edge/face (depending on mode) to the mouse cursor is selected
• Expected behavior: Deselect All action performed, leaving nothing selected, both in select and transform mode
• Precedents similar to expected behavior:
  • Clicking a blank area in the 3d viewport in edit mode deselects all (expected behavior)
  • Clicking a blank area in the 3d viewport in ocject mode deselects all (expected behavior)

Exact steps for others to reproduce the error

1. Enter UV Editing layout
2. Enable UV and mesh sync to show all UVs
3. Left-click anywhere in the UV viewport