Smarty cache is great for server performance on production but is annoying on developpement.
Hopefully, you can enable or disable it.

On prestashop 1.3.x or less, you have to edit the root/config/smarty.config.php and edit these 2 lines

$smarty->caching        = false;   // to pass "true" when put into production
$smarty->force_compile  = true;    // to pass "false" when put into production

On prestashop 1.4.x or more, you can do it directly on the backoffice, preference tab, performences subtab