Problem: Exchange rate in Update rules with DELTA mode

Question

Hi experts,
During the loading since the ODS13BIL towards the CUBE, I use in the update rule the function
"CONVERT_TO_LOCAL_CURRENCY" to convert a currency. 
The loading mode is DELTA.
If I modify an invoice in the system source (R/3) for example:  "change on" (0CH_ON), during the loading delta since the ODS towards the cube, the exchange rate is reversed (sign), which implies that the values of the ratios during the conversion with the function module " CONVERT_TO_LOCAL_CURRENCY" are false. 
How could I resolve this problem?
Example:
1-First load:
R/3:    
Key figure 1       :100
Exchange Rate      :-1,2
Document currency  :USD
Local currency        :EUR
Change on          :00.00.0000
ODS13BIL:
Key figure 1       :100
Exchange Rate      :-1,2
Document currency  :USD
Local currency        :EUR
Change on          :#
CUBE:
Key figure 1  :100/1,2
Currency      :EUR     
2-Seconde load:
R/3:    
Key figure 1       :100
Exchange Rate      :-1,2
Document currency  :USD
Local currency        :EUR
Change on          :06/01/2006
ODS13BIL:
Key figure 1       :100
Exchange Rate      :-1,2
Document currency  :USD
Local currency        :EUR
Change on          :06/01/2006
CUBE:
Key figure 1   :100/1,2
Currency       :EUR
and
Key figure 1   :-100*1,2      <-- False
Currency       :EUR
Thank you for your precious help.

Answer 1

Hello,
Thank you for your answer but that still not works: Give erroneous data is corrected but the data which are not erroneous become erroneous.
I think that if I manage to return the field "Exchange misses" (0EXCHG_RATE) nonmodifiable by the DELTA mode, I cross that will resolve the problem. 
With what is used following fields in the definition of the ODS, and it is what impacts it on the existing data:  "Non cumulative value" et "Cumulative value"
thanks a lot.