Answered
Dear Developer(s)!
Latex-Text, which you can even see in the preview (not just within the file) http://www.geogebratube.org/material/show/id/50153) is cut away / not completely displayed on the worksheet: http://www.geogebratube.org...
...
The same problem 
Does it work if you use \cr instead of \\ for the line-breaks?
Heureka!
With \cr ist works!
By the way - for some reason it didn't work when I made extra textboxes for each line!
... as one can see in this copy:
http://tube.geogebra.org/st...
\begin isn't supported. Please use TableText if you want to make tables
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