Code for test:
var sr = mapView.Map.SpatialReference;
var extent = mapView.Extent;
Steps to reproduce the problem:
1. Create new project. Variables now will have values:
2. Add layer with WGS84 spatial reference and zoom to full extent (the issue will be without zooming too). Now execute the code above:
We see that spatial reference now is WGS84, but extent coordinates doesn't correspond to WGS84. Max extent for this sr must be -180 -90 180 90 in degrees, but the values from screenshot are obviously wrong.
More than that I can't project extent to WGS84, because it's already in WGS84, so coordinates still the same!