Blender Version
Broken: 2.79 to 2.83 alpha
Worked: 2.79 to 2.83 alpha (with UV Sync turned On).
Short description of error
When deselecting an edge or a face in the UV Editor, it deselects not only the edge/face but also their vertices. So it ends up deselecting more edges/faces than intended. This only happens when UV Sync Selection is turned off.
Exact steps for others to reproduce the error
Open attached file.
In the uv editor, Shift click any of the selected edges to deselect it.
See that the other edges were also deselected, thats the bug.
Now still in the UV editor:
Press 3 to change to face select mode.
Press A to select all UV faces.
Shift click to deselect a UV face, the other ones will be deselected, thats also the bug.