I am experiencing a minor issue in Terragen V2.4 build 188.8.131.52 where the Navigation Widget Move Forward and Move Backward buttons don't work if the camera's rotation.x is set to -90 to create a top view.
To reproduce this issue:
Open Terragen V2.4 184.108.40.206.
Change the Render Camera Rotation.X from the default of -20 to -90, to give a top view.
LMB Click on the Navigation Control Widget.
LMB Clicking on the Move Left and Move Right buttons works as expected, but when you LMB Click on the Move Forward and Move Backward button the camera does not move.
If you change the Camera Rotation.X to -90.0001, and in the 3D Viewport change the back to the Render Camera from the Perspective Camera the Move Forward and Move Backward buttons work as expected.
This bug is not present in the current Terragen 2 Free edition Build 220.127.116.11.
Please could somebody confirm and investigate.