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If you submit a bug that happens when you play a quest, submit a copy of the quest that it's happening in. Otherwise, time that the developers could use to fix the bug would instead be used to try to duplicate it and there is often something else associated that is causing the bug which isn't getting duplicated.

There are several services available for this: ZShare, FileSpace, etc.

Failure to do this will result in your bug report being moved to Limbo.

Also, screenshots would be helpful as well, but should in no way be considered replacements for a test quest.