Having groups with the same name but on different event sheets included to one layout will treat them as one and same group.
One layout - 2 event sheets included
First event sheet have group called "Upgrades" (Activate on start) and some stuff inside.
Second event sheet have group "Menu" (Not active) and sub-group called "Upgrades" (Not Active).
If you do something to Activete group "Menu" on second event sheet, sub-group "Upgrades" will automatically be activated becouse there is group with same name - active on start - on different event sheet.
Don't think it's a bug really, more like a cheat. Editor will not let you use same name for two different groups on same event sheet. However you can make group with the same name on other event sheet and include it to first one.