Defeating the Vaal oversoul twice?

The other day I got to the ancient pyramid where you defeat the Vaal oversoul, after about an hour I finally destroyed him, and there were a few rare/ enchanted items on the floor... but unfortunately they were useless to me. So then I opened up a portal to town so I could sell the items and I spent too much time in the town, as a result my portal closed. I thought "Oh, that's okay I'll just work my way back up to the top of the pyramid. no problem" but when I eventually got back up there, I had to defeat the Vaal oversoul again.

Basically my question is: Has anyone else encountered this problem? 'cause this has really annoyed me!

many thanks.

don't risk instance resets after major boss fights.
if you need to sell stuff and the rest of the loot is worthless, just go ahead into Act 3. there's a waypoint in there just like there was at the start of Act 2.

on a personal note: I love the Vaal boss fight so much, I would do it endlessly given good enough server synchronization. by far the best boss in the game.

Oh... okay, thanks. I'll remember that in future, haha!

And yes the Vaal was a good challenge, and a couple of times he killed me as soon as I entered his lair! I'm just annoyed that I made such a stupid mistake and now I have to do it again *facepalm*