MegaTerrain Editor bug

So i recently redownloaded TGEA from the site ...

* installed it
* launched the T3d Demo
* loaded a new misson
* replaced the legacy terrain with a MegaTerrain
* Resaved it under a new name
* added the waterblock from the altasdemo (copy/paste the datablock in the *.mis file)

and began to edit the terrain when i see this comming up from the water:

Now i haven't done anything at all besides what if stated above ... and relighting/loading the mission/client don't help.