In skin1/customer/main/products_t.tpl, look for this bunch of code and adjust accordingly:
Code:
{if $discount gt 0}
<FONT class="MarketPrice">{$lng.lbl_market_price}: <S>
{include file="currency.tpl" value=$products[product].list_price}
</S></FONT>
{/if}
That is from the 4.0.12 template, and it looks like the space is already there. You may have inadvertently removed the space if you deleted those <s> tags.