When you copy some data into Office document by using Office 2010, there is always a Paste Option for you to choice if you want to discard format. If the Option doesn't show up, you can turn it on by clicking File -> Options -> Advanced -> Cut,
copy and paste category -> check the first item.
I have no idea why Excel choice to discard format when pasting by default for a particular user. But he/she may fix the issue by manually picking "keep Source formatting".
In addition, for those end-user level question, I would recommend you to post it in Excel Answer forum for better response.