what are the conditions that cause hotsync to flip from enabled to disabled?

I know you can disconnect and reconnect the usb connect, stomp your feet three times, and say a blessing, but what are the actual causes and effects.

I know this is an oldie, sorry, but I've never understood this and it's annoying in the extreme.

I'm syncing with a macintosh running OS X 10.3.6.

thanks.