Nether reactor dissapeared

I created the nether reactor,activated it,then left the map a few minutes later.i go back on that map an hour later,and the big nettherack temple was gone
What I expected to happen was...:
Come back on the map and be able to see it.

What actually happened was...:

It disappeared

Steps to Reproduce:
1. Build the nether reactor
2. Activate it
3. Leave the map a few minutes later and return to the map