Answers:
1. Incorrect. This happens to any skill and regardless of whether a material from your back is used.
2. This happens more and less often depending on either lag or frame rate - unsure which, though more inclined to think that it's the frame rate. When nobody is around, almost never happens. When another player is close to me, it happens a lot. When 2-3 players are near, happens on 4 out of 5 attempts. I think it also depends on the amount of trees and architecture that's nearby, but I'm unsure if this is true.
3. I imagine it can be, but it would take for multiple people to be together in one place. Bug almost never occurs when I craft alone.
Summary: log in lots of people next to you and have them run around and do things (moving logs around the area, gathering grass, running with carts, etc etc) and try to craft in the middle of all that - unless you have one of those monster computers, I'm sure you will catch the bug sooner or later.
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