[Tom Bunch]

It sounds like you're describing what I like to refer to as "The Beginning of Time". Or, for projects scheduled backwards from a fixed end, "The End of Time".

People were confused about why there was this line on the left side of the gantt chart that tasks wouldn't start before. You could always make them start later, but no matter how hard you drag them, they wouldn't go earlier. That's because the project start date is an implicit start no earlier than constraint on every task in the project. We decided to go ahead and draw it. You can turn it off (and on again) using the View -> Gantt -> Show Project Start menu item.

Note that when you drag a task around as you have, you set a start constraint on it. In general, start constraints (or any kind of constraints) should be used only when there is some real world reason that task cannot begin earlier (or whatever). It's a bad practice to add constraints or dependencies to tasks if they do not accurately model a real world constraining factor. Just a little aside there.

-Tom