Excel negative number format problem

After upgrading my MacBookPro Retina to Yosemite from Mavericks, Excel 2011 no longer provides for the conventional default formatting of negative numbers using parentheses, e.g. where the number -1234 would be displayed as (1234). Per a post over at Microsoft this is associated with the Yosemite upgrade for a number of Excel 2011 users. Excel derives the default number formatting--i.e. whether to use the minus sign or parentheses--from the regional settings in the underlying OS. I have checked my settings to ensure that they are US and US$. I have tried changing the region back and forth from different regions. I have tried updating and then uninstalling/reinstalling Office 2011. None of these worked, for me or the other posters on the Microsoft site. I did not see a thread on this topic here, so I am posting the issue in the hope that someone has a fix or that Apple will address this in a patch for Yosemite. I am aware of a workaround using custom number formatting in Excel, but this is a big pain, particularly when working with existing spreadsheets that were not set up to deal with this issue.