Drowned won't de-spawn, burn in sunlight, and is non hostile

On my Private server I found a drowned that has been living on top of one of my players basses for many in game days. It has no name tag, It does not attack players. It stands out in the sunlight. It isn't a big problem but it is strange.

 

No one has tried to kill it yet because we are all just curious to see how long he survives on the server.

 

We usually play on hard but we have set the world to peaceful for a few builds. I wonder if changing the game mode while he is out of render distance had something to do with it?