pantheon-terminal is set to periodically update a saved state variable with your terminal's position. You can flush it out with the following commands:
gsettings reset org.pantheon.terminal.saved-state opening-x
gsettings reset org.pantheon.terminal.saved-state opening-y
but unless you run these right before you open a new window, any additional windows are coded to overlay the original. (One would think that they should at least cascade... I think that's worthy of a bug report.)
Your only other option would be to download and recompile pantheon-terminal while commenting out the lines that recall the positional saved state. This would mean commenting out the following two lines in /src/PantheonTerminalWindow.vala
and recompiling as you wish:
if (restore_pos) {
int x; # = saved_state.opening_x;
int y; # = saved_state.opening_y;
if (x != -1 && y != -1) {
move (x, y);
} else {
x = (Gdk.Screen.width () - default_width) / 2;
y = (Gdk.Screen.height () - default_height) / 2;
move (x, y);
}
}
A jury-rigged alternative would be to only open Terminal from a custom keyboard shortcut (or link) and to have that shortcut trigger a simple script that resets those two variables and opens another instance of pantheon-terminal. (Let me know if you would like help with that.) The best solution would likely to be filing a bug report so we can see if we can't get this entire function to be toggle-able in org.pantheon.terminal.settings
...