Zombie Pigmen spawn in Overworld Nether Portals and immediately are sent back

Hello,

I am working on making a big gold farm in the newest version of Minecraft PE / Bedrock on a Realm server. After creating the 1st portal, as pictured, I started to notice that while zombie pigmen are spawning, they immediately are sent back to the Nether. Little hard to noticed at first, since the spawning is very brief as they re-enter the nether almost instantaneous. They aren't moving away and moving back, they are just spawning and then being sent into Nether.

I haven't really noticed this issue yet with the nether portal we have at our town spawn area, but I haven't had a chance to clearly monitor to see if it's happening there as well.

Thanks.