Created attachment 80510 [details]
Screen shots of Steps To Reproduce.

[Procedure for reproducing]

1. Start Calc.
2. Input numeric values to cells A1:B10.
3. Set format codes of B1:B10 to "0.000;[RED]-0.000".
4. Select cells B1:B10, click "ChartWizard" and "Finish" it without change. (Any of these charts will do.)
5. Set format codes of A1:A10 to "0.000" .
6. Save and close the Calc.
7. Open the file again.
8. Format codes of A1:A10 are return to "Standard" from "0.000".


[In case of format codes are return to "Standard".]
--------------------------------------------------------
Format code of A1:A10		|  Format code of B1:B10
--------------------------------------------------------
0.000;[RED]-0.000		|  0.000
0.000;[RED]-0.0000		|  0.000
0.0000;[RED]-0.000		|  0.0000
0.000;[BLUE]-0.000		|  0.000
0.0000000000;[RED]-0.000	|  0.0000000000
0.000;-0.0000		|  0.000
#.0;[RED]-0.0		|  #.0
------------------------------------------------


[In case of format doesn't change.]
--------------------------------------------------------
Format code of A1:A10		|  Format code of B1:B10
--------------------------------------------------------
0.000;[RED]-0.000		|  0.00
0.00;[RED]-0.00		|  0.000
0.000;[RED]-0.000		|  0.0
0.000000000;[RED]-0.000	|  0.0000000000
0.0000;[RED]-0.000		|  0.000
#.0;[RED]-0.000		|  0.000
0.000;[RED]-0.000		|  0.000;-0.000
--------------------------------------------------------

From the above, 
format of cell which has same setting as base data of graph and format code specified only for positive number part 
is return to "Standard" when format code of data cell that referenced by the graph are;

- More than 3 decimal places and using "0" after the decimal point.
- Using "#".

I attached problem sample files. Please read these. 

Sincerely.