The following error was reported by minohaka on http://irclogs.wildfiregames.com/2019-11/2019-11-05-QuakeNet-%230ad-dev.log
```
ERROR: JavaScript error: gui/session/selection.js line 88TypeError: property 274 is non-configurable and can't be deleted
EntityGroups.prototype.removeEnt@gui/session/selection.js:88:2
EntityGroupsContainer.prototype.update@gui/session/selection.js:496:5
updateGroups@gui/session/session.js:672:2
updateGUIObjects@gui/session/session.js:657:2
onSimulationUpdate@gui/session/session.js:629:2
__eventhandler56 (simulationupdate)@session simulationupdate:0:1
```
From the replay file we can see that quickloading was used, from which one can derive how to reproduce the error:
1. starts singleplayer match
2. select an entity
3. cltr+1 to assign it to a control group
4. shift+F5 to perform quicksave
5. shift+F8 to perform quickload
6. delete that entity
Consequently the error was introduced by rP22922/D2302 providing an immutable JS object whose ownership was taken over in `session.js` `restoreSavedGameData` in `g_Groups.groups[groupNumber].groups = data.groups[groupNumber].groups;`.