Depreciation while doing impairment

Hi Team ,

We have a few assets that need to be impaired and also we need to override the current depreciation amount. 

Below is the example.

Asset No  : 123

Date in Service : 01-Jan-2013

Cost : 12,000

Life : 10 yrs

Current open period : Dec-15

Depreciation until Oct 15 : 12,000 / 120 mths * 22 mths = 2200

Depreciation per month = 100

Impairment amount = 2000

We put a depreciation override amount of 0 in the month of Nov -15  due to business issues and impaired the asset in current open period DEC -15 . In Dec -15 we put an override depreciation amount of 350 to catch last month depreciation and other calculations ,but when we loaded the impairment the total depreciation as of Dec -15 calculated is 2200 (as of Oct 15 ) + 0 (Nov-15) + 100 (dec-15 ) = 2300 instead of  2550.