I had a similar problem. Had a portal in mistlands that was buried after the update. The portal stayed in tact though underground. If I use the portal I show up on the ground somewhere above I believe. So its basically a one way portal. I thought of digging under to look for the portal, but decided to keep it there hidden to trick friends :+)

I have a feeling this is what happened to you. If you make it back to base and the Mistlands1 portal is still active then that would confirm it is the same as my world, you have an active portal underground and when you use it it pops your character to the surface.