I would like to clarify my findings again. Your sample file is loaded and saved again using Aspose.Cells latest version. Now there are two files one is the original file and the second one is the saved file (by Aspose.Cells). As per your statement, your original file shows integer value only whereas the saved file shows complete float value i.e. integer and decimals both.
I opened these two files side by side in the following environments:
Excel 2010, Windows 7 - BOTH the files show decimal values
Excel 2010, Windows 8 - BOTH the files show decimal values
Excel 2016, Windows 7 - BOTH the files show values without decimal
Excel 2016, macOS - BOTH the files show values without decimal
These results at our end show that before and after saving the file, there is no difference if both the files are tested in the same environment. Hence it does not seem to be an issue with Aspose.Cells. On the other hand, if we see the above results, Excel 2010 shows decimal values in both the files but Excel 2016 does not show decimal values in both the files. Hence it seems to be the difference in the behavior of Excel while handling this custom formatting string.
Now coming back to your statement, you mentioned that in the same environment (Excel 2010/Windows 7) original file does not show decimal whereas saved file shows decimal values. This behavior is not reproduced by any means here. You may please share an image where both the files are opened side by side. We will try to investigate it more (if possible).
Hope this clarifies the situation.