LO ignores cell formatting

I have tons of Calc docs originally created with Apache-OO (under Widows). Now I moved to Ubuntu 15.10 and LO but my cell formatting does not work, e.g. negativ numbers to be shown in red. Any help is greatly appreciated!

When you look at Format, Cells for the cells affected, do they still show the correct Number format? Is this one of the default number formats within LO or is it a format that was in OO but not in LO?

Try creating the same number format again in a new cell and see if the other cells using that number format start to work again.