Thanks @creece and @Sam-I-Am - I figured out an easier way. The Item Fulfillment records that were updated recently from Picked to Shipped converted the "Posting" from N to Y for these records - thereby changing the GL impact in the reports. I just had to revert the IF record back to Picked so that it becomes non-posting - for the affected records. Luckily, there were not a lot!

ntiwari1309: that seems like a bug in the system.. after the period is closed it should not post it