The same way it knows not to move the object when you press F3. If you're in "connector-mode," it draws connectors.
Basically, we're asking for an "automatic-F3," to prevent you from having to press the F3 key after each connector. My proposal is to turn this feature on by double-clicking the connector icon in the toolbox.
Of course, using F3 is pretty fast if you just hover your finger over the key while drawing connectors, so this probably is not a very high priority feature. There's an easy and effective solution already in place.