When I close the minecraft game completely,reopen it, and launch my world, theres a random nether portal near or in my base, it gets really annoying because i have to go into creative to destroy them, any ideas what is causing this?

I didnt try the observatory template, but the default one had the problem even when i deleted my game folder and reinstalled the modpack completely

What version of java are you using? And any logs you can provide from an absolute clean install to the issue presenting itself would be most helpful.

Same with a new world and both templates?

Id really like to see this in a reproducable way since theres just really no mechanic i can think of that does this stuff.

@vekenti maybe try building on near by where you don't care.
Overall we will need to find a way of reproducing it to get any further.

The nether portal seems to only spawn when you load the world with a different account.
So create the world with account X and then load it with account Y