Operating system: Win 10 Pro
Graphics card: nVidia GeForce GTX 1070ti
Broken: tested in 2.80 stable and 2.81-dcad1eb03ccc
Short description of error
In Edit Mode Select -> Select all by Trait -> Interior Faces does not select all expected Faces.
Exact steps for others to reproduce the error
In the attached blend file try to select the interior faces by trait and nothing happens. The object was created by moving a default cyclinder and UV sphere into each other and merging the vertices at the spheres equator by distance. After the merge the top face of the cylinder is selected by trait as expected while the lower faces of the sphere are not.