It's less egregious, but remember that clicking away from the list (e.g. to close it) is also often an input option. Even though that's a lower input priority it could still disrespect the user's desires if they were trying to leave the list.

You are right, then perhaps leaving a placeholder area which is already bigger to accommodate some additional content? Eg. showing 3 actual lines plus a placeholder of additional 10, which might remain empty (but shows a loading indicator before)?