I don't know what you mean by "inference engine"
I just tried again under Ubuntu and didn't notice any issue while drawing rooms, even with a virtual machine running under Parallels Desktop. There must be another issue on your computer.
You could also try with an older version of Sweet Home 3D because the last version comes with a more recent version of Java, but I would be astonished that it works better.
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Emmanuel Puybaret, Sweet Home 3D creator
