It seems that the mouse coordinates are not interpreted in the same way if not using the default perspective view. I get the popup message "Path blocked". If I zoom in, I can walk. If I zoom out "Path blocked".
Seems to happen around a green bush model in Zanely Downs.
These are the settings I used:
I noticed also monsters sometimes seem to get stuck (before I played with the perspective) which may be a related bug. Like if they have no direct line of sight they stop running after you.