WHY DO SOME ASSETS CONTINUE TO HAVE DEPRECIATION EXPENSE AFTER BEING DISPOSED?

We have several assets that continue to record depreciation expense (Depreciation Close) after they have been disposed.  In looking at the assets in question, the disposal did not reverse the accumulated depreciation, rather it took the cost as the loss.  The disposal code used includes A and N and the Fully Depr SW is N.  Retirement Status includes C and N.  Is anyone aware of other fields that could cause this to happen?  These seem to happen randomly as we other disposals with the same codes the have reversed the accumulated depreciation and stopped calculating the depreciation.  The Open Trans