I don't think this has much to do with your code as I think its just how IE works, however...
I assume you are referring to copying 5 vertical cells from Excel? Copying 5 horizontal cells works OK for me in all browsers.
I only see a 'problem' with text INPUTs. TEXTAREAs work OK for me. (But you see the same problem with TEXTAREAs as well?) This can be expected IMHO. If you are trying to paste essentially multiline data into a text INPUT it is reasonable to expect there to be a problem. INPUTs cannot accommodate newlines. This seems to work in other browsers as they appear to remove the newlines before the data is pasted.