The only differences are difficulty of enemies, loot dropped by enemies, and obviously the lack of other players around.
The glitch that happened to me:
I had two golden keys. I used one playing single player. I later joined my friend in his world, and with one key left, I somehow had unlimited access to the golden chest. NYCHitman1 joined me later, but with none of his own keys remaining, he was not able to open the chest. Obviously, it makes a difference of whether or not you have any existing keys.
Here are the conditions in which it happened, each highlighted individually:
-I had one key remaining.
-I was playing in another players world.
-That other player did not have any pre-order content.
-I had the pre-order content.
I do not take responsibility if you waste any golden keys trying to replicate this glitch!
When I obtain another golden key, I will try replicating this again myself.
Update: Just a quick search, this is a confirmed glitch on the interwebz. Take advantage of cheat-free freebies while you can, before they "fix" this!
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