haha ce patch 0.10.4
Item drops from monsters are now calculated based on the number of players nearby (13 metres - around six tiles, which is approximately a screen) rather than the number in the instance. The quantity of drops is based on the minimum of the number of players who were around at the start and end of the fight. This means that if you spawn a boss alone before bringing in friends to help (or if the friends leave during the fight) then it will only drop enough items for one person.
a+ le multiboxing <3