Yes, the typed version is definitely better in my opinion too. I'd say that you're right, and that QTBUG-15641 is related (although I can't remember enough of the QtQuick1.x code to say why the cached typedata resolution could fail for inline components, or how that might be reproduced in your use-case).
Unfortunately, we're focusing purely on Qt 5 at the moment, and that bug in QtQuick1.x is unlikely to get fixed soon.
Another possibility is to use "property QtObject propname", instead of "property variant propname" -- at least then you get the typechecking for QObject-derivedness, so attempting to assign integers or strings etc will fail. It's not perfect, but it's better than nothing, I guess.
Cheers,
Chris.