Mr Peabody and I used the Wayback Machine to remind us how tax preparers were thinking back in 1997.  (Actually, I just did a Google search for a 1997 IRS Pub 334, and it's right there online.)  Back in the good old days, straight line depreciation required a determination of salvage value.  If salvage value was less than 10%, it could be disregarded.  But what it sounds like to me is that this $50,000 item had $22,000 of salvage value, in the mind of a 1997 accountant, so only $28,000 was being depreciated.  

I don't remember worrying about salvage value with residential rental property, but maybe they were trying to minimize depreciation to avoid recapture.  What exactly was this improvement?  Are there other items on the depreciation schedule that suggest a concern about salvage value?