Removed lemming fixed in commit 0e7ea49. Teleporting lemming fixed in commit 50b52b7.
There is still a slight oddity for one frame with a Laserer who goes through a portal. Given that a very specific and unusual setup in the level design is required to achieve this, and it would be a fair bit of effort to make a fix that doesn't risk breaking other things, I'm leaving that case as-is.