Never ever use in UnrealEd Undo for Paste action!
In UT exists very weird bug: https://github.com/OldUnreal/UnrealTour ... issues/616
In fact this overwrite memory, so duplicate actors it is not only possible side effect.
Your work can be destroyed in a lot ways.
So if you use paste (even empty text) forget about undo.
Undo history cleared on any build, so if you have habit press ctrl+z, better rebuilt light or paths, for block possibility screw up your work.
If you fall into this problem, better export all to t3d and import back as new map. But be ready for lost of some things in random places. It can be anything. or even nothing if you lucky.
If you really not lucky properties of actors be screwed too and appear in t3d, so moved on new map too.
OFC with time in some upcoming patches (I hope in v469c) issue be fixed and you can use Undo for Paste. But before that - avoid it.
