[BUG][Editor] Copy-pasting groups can cause editor errors

[Apjjm]

Copy + pasting nested groups can cause various unexpected editor behaviours:

• Copying a group between editors can cause the editor to produce a series of errors (per peice in the groups), for some nested group structures
• If the editor has ever loaded level with a given group, copying a group with an identical name into the editor may not give the expected layout even if that level isn't loaded

In the case of (1) it seems to be primarily caused by groups that have a structure that is a bit like:

Code Select Expand


Badly Behaved Group
   | Group A
   | Group B
     | Group A (again)


I have attached a level that reproduces this bug. The minimal steps to repoduce this are:

• Open the editor twice
• In editor 1, open the level
• Copy-paste the group into editor 2

For scenario (2) the minimal steps needed to observe this are:

• In editor 1 (that currently has the level open) go File -> New
• Edit the level file on disk with some noticable terrain change (e.g. double the X position of a terrain piece)
• Load the level (new version) in editor 2 - it should look different
• Copy-paste the edited group into editor 1 (the editor with the blank 'new' level) - it will have the old layout still