Mob trap for XP limiting mobs before killing them off

The drop-down menu above says 1.11.0 is "unreleased" for Realms, but that's what I've been signing into (including the updated 1.11.2) since first released. This bug/issue has been a problem since 1.11.0.

In the Realm I play in, someone created a spider mob trap (for XP) using a spawner found in an abandoned mine. Before 1.11.0, the number of spiders a player could accumulate at any one time was limited only by how much lag was created on the server. One of our players had over 400. I reached over 300 once.

Now, I can barely get past 80, if that, before the spiders start dying off on their own. I have to close the trap, accumulate the dropped XP, then open it again to gain more XP. When using this to mend tools and weapons, it's quite a chore to do it in small chunks like this.

Is this a bug, or is it a purposeful change in the game mechanics in the 1.11.+ updates?

I'm in the process of duplicating the trap in single player mode to see if the problem exists there as well.