[Therion] Extended elevations with survex data

Hi, I'm trying to create an extended elevation of a cave. I have the centreline data as survex files and have created an extended version of the .3d using the survex "extend" command with a specfile to specify at which points the elevation switches direction. I have created a .th file like so: survey texa-elev import texa_extend.3d input elev_top.th2 endsurvey but therion doesn't respect the changes of direction in texa_extend.3d and extends it all out to the right which doesn't correspond to the drawings in elev_top.th2 and produces very corrupted output. Is there a way to correct this and tell therion where the switches in direction are? Cheers, John