oh yes, you should have got the LB then. But as IRCTC don't have the authority to prepare charts and I guess the charts are being made at divisional levels. Then maybe IRCTC don't pass on the info of your preference to the zonal level or divisional level and so the chart preparing authority allots you berths randomly.
This has happened to me also many times. I have got the most averted berth by me ie. middle berth despite the LBs being vacant after chart.