Thanks for the bug report
That may explain why the bug #415 doesn't happen all the time. It must depends on how many new words you entered during a session of Sweet Home 3D. If there are too many words (more exactly if the list is longer than 8092 characters), Java will refuse to write it in preferences along with other values like the recent files list, the recent colors…
It will be fixed in the next version.
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Emmanuel Puybaret, Sweet Home 3D creator
