The chances of this happening again are probably really low, But I had this occur earlier today. It's possible for harvester to spawn right on top of somebody, Pushing them to the side so the Harvester can land, And then attack. While this doesn't sound like an issue, It's possible to glitch outside the map using this tactic. Earlier today I was playing the mission, and looking for the various puzzles hidden around the map. While trying to avoid some Scarabs, I leaned against the left edge of the map. At the same time the Harvester warped to me, When he landed he pushed me left, Through the wall and outside the map. I took various screenshots, Some rather interesting.

Me outside the map, With somebody still inside the map:
- http://cloud-4.steampowered.com/ugc/577899631452563398/BC312E88B8BD30B62...

Me at the edge of the map, With The Harvester. (Not the actual edge, But as far as the scenery goes.
- http://cloud-3.steampowered.com/ugc/577899631452546691/20D9B7BB4FF2CBEEC...

Me so far out of the map, I actually found the Radar's limits. (Look at the mini map)
- http://cloud-4.steampowered.com/ugc/577899631452553735/446B0D8F57CDA72EB...

And finally, Me so far out of the map that not even the radar has a signal.
- http://cloud-2.steampowered.com/ugc/577899631452556360/702AD568BDB19C9C7...

It's possible to have The Harvester follow you outside the map, You can walk forever and he'll still follow you. (Provided you're within range of him, If he warps away he won't be able to relocate to you) On top of that, With a properly equipped gun you can abuse this tactic further by farming Harvester Kills for that rare drop.
I actually did find this glitch rather interesting, Mainly because it showed me what exactly are the limits of the game. It's possible to walk so far away from the map that the icons will only appear as a blur. Regardless though, This does need patching. While it is a rare event, It's very easy to abuse when it occurs.