Sifter of Skulls only creates tokens on next upkeep

I had a [[Sifter of Skulls]] out and my opponent killed one of my other creatures. Instead of getting the 1/1 Eldrazi Scion right away, it triggered on my next upkeep and I got it then.

Start by locating the Java implementation of Sifter of Skulls and inspect how its creature-death trigger is scheduled, especially the upkeep handling described in the report. Done means the Eldrazi Scion is created immediately when another creature dies, rather than during the next upkeep.

Written by the indexing model from the issue text.