System Information
Operating system: Win64
Graphics card:

Blender Version
Broken: blender-2.80-40412499433e-win64 2019-03-09
Worked: (optional)

Short description of error
3D Viewport: Hitbox for tool shelf does not respect collapse of sections, blocking Orbit and allowing resize in odd location

Exact steps for others to reproduce the error
New Default Startup
Expand Tool Shelf (horizontally)
Collapse Tool Shelf sections (vertically)

UI looks like this:

Viewport region below toolshelf (see pic, grease pencil marked area), does not respond to middle mouse button (cursor changes to toolshelf colon cursor when MMB pressed). LMB, RMB works as expected.

Below toolshelf left edge (vertical grease pencil line) cursor changes to horizontal resize and LMB does tool shelf resize.