1) Create several sprites and add them to a family.
2) Create a new event.
Result = You can't create system conditions/actions.
Works fine here. The families appear before the system object in the list, but the system object is still there. Does it completely disappear? Can you email a .cap with a disappeared system object to ashley@scirra.com?
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Cap it's unuseful, I tried it with several caps, and fresh ones. I suspect it's a bug with Vista.