My latest attempt.
Two hours ago I created a fresh install of the Alpha. I attempted to create a terrain with nothing but land and water, no bases. In previous patch version, a base #1 was added in the center of the terrain, but not in this version.
I'd saved and been unable to reopen the terrain. I still can't.
I cleared the cfg file (actually I think it was still a blank terrain on launch) and created a new terrain. This time I added field 1 and 1 road which I named, saved and successfully reopened the terrain myterr2.
Then I converted an AH2 terrain I'd been working on. It crashed the TE. I copied the content of the working myterr2.tra file into the tra file of the converted AH2 terrain and it then opened, saved and reopened without complaint.
I successfully reopened myterr2, and while it was up, reopened the converted AH2 terrain.
715 provided the hint for this yesterday. I'd not stumbled upon the right combination of steps to duplicate it and make the TE work the same consistently.
A followup:
I transfered a backup copy of the avachanl terrain into the ah3terr folder. It successfully opened. I saved. It crashed the TE upon reopening but since the cfg file was updated...
To solve the problem, I again pasted the content of the myterr2.tra into the avachanl.tra.
Now I get to play with roads like I was supposed too.
But that'll have to wait until tomorrow.