What is causing Bloomberg image to appear on Excel spreadsheet?

Some workstations have been updated to Windows 7 on the trade floor. They are running Bloomberg and Excel, just like on the previous XP machines. However now at random times in the day for few seconds, when an excel spreadsheet is opened, parts of the Bloomberg application appear on the spreadsheet. To be more specific, small patches on the screen show what would have been on the Bloomberg application in that spot on excel.

The traders received new machines, which has a more powerful graphic card, more ram, more processing. The monitors have not changed.