Currently when you click the "Put on server" button load a "world" you are being told that it would take one minute.
The problem is the "world" will not load until you restart the server completely, which takes about 15 minutes.
This is clearly a bug. The fix is quite simple.
Fixing it would help progressing faster as you/your child would not care much about messing the "world" and would feel free to experiment.
The description and discussion is here http://forum.learntomod.com/t/world-wont-change/75567
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