Unable to assign multiple hosting accounts to domains while ordering

[Nullified]

I am using a custom order form that is being developed (base model is boxes). For some reason when I order multiple domain and try to add hosting for a second domain it reloads the product selection page and reset everything in the orderform.

<div class="productBox">
<div class="boxBG">
	<table width="100%" cellpadding="0" cellspacing="0" border="0" class="packageList" align="center">
		<tr>
			<td class="topBarLeft"></td>
			<td class="spacerTop"></td>
			<td class="topBarRight"></td>
		</tr>
		<tr>
			<td>
				{foreach key=num item=productgroup from=$productgroups}
				<form method="get" action="{$smarty.server.PHP_SELF}">
				<input type="hidden" name="gid" value="{$productgroup.gid}" />
				<input type="button" value="{$productgroup.name}" onclick="submit();" class="selectButton" />
				</form>
				{/foreach}
				{if $loggedin}
				<form method="get" action="{$smarty.server.PHP_SELF}">
				<input type="hidden" name="gid" value="{$productgroup.gid}" />
				<input type="button" value="{$LANG.cartproductaddons}" onclick="submit();" class="selectButton" />
				</form>
				{if $renewalsenabled}
				<form method="get" action="{$smarty.server.PHP_SELF}">
				<input type="hidden" name="gid" value="{$productgroup.gid}" />
				<input type="button" value="{$LANG.domainrenewals}" onclick="submit();" class="selectButton" />
				</form>
				{/if}
				{/if}
			</td>
			<td class="spacerMiddle"></td>
			<td height="100%">
				<table width="100%" height="100%" cellpadding="0" cellspacing="0" border="0" align="center" class="packages">
					<tr>
						{foreach key=num item=product from=$products}<td class="pacakgeBox">
							<h1>{$product.name}</h1>{if $product.qty!=""}: <em>({$product.qty} {$LANG.orderavailable})</em>{/if}
							<ul>
								{$product.description}
							</ul>
							<center><form method="post" action="{$smarty.server.PHP_SELF}?a=add"><input type="hidden" name="pid" value="{$product.pid}" /><input type="submit" value="{$LANG.cartselectproduct}" class="orderButton"{if $product.qty eq "0"} disabled{/if} /></form></center>
						</td>
						{/foreach}
					</tr>
				</table>
			</td>
		</tr>
		<tr>
			<td class="bottomBarLeft"></td>
			<td class="spacerBottom"></td>
			<td class="bottomBarRight"></td>
		</tr>
	</table>
</div>
</div>
{php}if (isset($_SESSION["cart"])) unset($_SESSION["cart"]);{/php}

{php}if (isset($_SESSION["cart"])) unset($_SESSION["cart"]);{/php}]

I notice that this is at the bottom of boxes orderform (which is the one I used to create mine, is this the issue? why would this be in there?

[Nullified]

After removing the php code that unsets the session data it works fine. Why the heck would that even be there in the first place?