Store Manager does not have the possibility to enable or disable "Leave Base Price" option when adding or editing Specific Prices.
Prestashop backoffice handles this option with a simple checkbox inside "Specific Prices" This allows to show or hide the original price without discounts
Apr 02, 2015
it seems about this option - see screenshot - presta-1-5-6.png
please enter Specific price - edit option - use "-1" value to set this value
this behavior was the same as in last versions of PrestaShop (1.4) - see screenshot - sprcific-price.png