Steps to recreate:
[LIST=1]
[*]File->New
[*]Click the Screen Enemies panel in the bottom left of the editor.
[*]
[*]Double-click a "(None)"
[*]Double-click "Aquamentus (Facing Left)"
[*]Click OK to dismiss Enemies window
[*]Observe Aquamentus (Facing Left) is now in the Screen Enemies panel.
[*]Quest->Defaults->Enemies
[*]Click 'Yes' to Reset all enemy/NPC data.
[*]Observe Aquamentus (Facing Left) is still in the Screen Enemies panel.
[/LIST]
Consider rewording the msgbox to say enemy map data will not be reset and dropping the word "all."