Portal won't let me go through...2 enemies remaining permanently

Warning: Possible spoilers ahead!

Hey everyone. So, I've encountered a glitch. On the 4th (I believe) level, the Lava Barracks, I cannot get through the portal. Once I activated it, as per usual I defeated the boss and all of the enemies on the level. Or, all in sight at least with my Engineer. However, it says I still have two enemies left to kill - but there are no enemies. :/

For those that have used the Engineer, you know the Harpoon attack always seeks the enemy. Always...no matter how far they seem to be, as I've discovered...I've attacked enemies that were in the other corner of the map. When there are no ememies, the harpoons go straight up and never come back...which is what they're doing now. I've resigned to the fact that I'm a goner and I'll lose my progress since it cannot be fixed yet, but...any ideas?

Here's a video, if that helps:

 

Better to keep bugs in the bug thread, they are always pinned to the top of the forums.