Created attachment 77738 [details]
A sample .ods file

In my Calc spreadsheets I use to format cells so the negative numbers appear as red (Format/Cells.../Category: Numbers and then I check “Negative numbers red”). I had no problem with all negative numbers using Calc up to version 3.6.5.2.

In Calc 4.0.x, if the negative number is the result of a function (i.e. the subtraction of two cells), when Ι save the file and open it again, the color of the number turns to black (default). [See Calc_4.0.x_Sample.ods and Calc_4.0.x_Sample.ods.pdf]

Strangely the problem appears only if Ι use the .ods file type. If i save the same file as .xls and open it again, all negative numbers have red color.  [See Calc_4.0.x_Sample.xls and Calc_4.0.x_Sample.xls.pdf]

I confirmed the problem using Calc 4.0.x in several O.S. (Mint13/MATE - Mint14/Cinnamon - Ubuntu12.04/Unity - Win7 Gr Home Premium).
Operating System: Linux (Other)
Version: 4.0.1.2 release