How far away are these players when they pick up the items? If they are rather close, this might be a mechanic of Minecraft rather than a mechanic of Spigot or Meepcraft. If this is the case, this is an "unintended feature" rather than a bug... in other words, the correcting of this bug would require an additional plugin that kept track of all entities that spawned as a result of a block-breaking event.
Now, if the player is far away (out of pick-up range)... this could be an issue.
