Making sense of the trial balance report

I'm trying to build my own trial balance report by retrieving PostingTransactionSummaries for every account for every period on the system and doing the appropriate arithmetic on them. However, my sums don't always agree with what is displayed on the Trial Balance report in the NetSuite UI. I have looked deeper into the issue and am confused by what the Trial Balance report in NetSuite is actually displaying. I am using the "testdrive" account with data unaltered since my account was set up (I'm developing an application that purely reads data from NetSuite).

If I look at the Trial Balance for Jan 2014, the account "1000 - Checking" is shown to have a balance of 116867.44. However, when I click on that amount to drill down to the account detail, it shows a balance of 113863.44 for that date. The difference seems to be the initial opening balance of -3184.00. Why is this initial balance disregarded by the Trial Balance report?