sorry was out doing errands but I see you found it...I guess add a readme explaining the limitation I guess would be my suggestion...I use Terragen 2.5 and it doesn't import displacements so I'm used to doing them after the import.

 

Once in a while I look around,
I see a sound
and try to write it down
Sometimes they come out very soft
Tinkling light sound
The Sun comes up again