Installing Microsoft Office 2011 caused arrows character to disappear. Why?

Prior to upgrading to Microsoft Office 2011 for Mac from Office 2008, one of my widgets (http://www.mirtchovski.com/code/environment.html) displayed a double-arrow character (⟷) in the text. Since installing Office it has been replaced by a question mark in a box. I haven't encountered this problem elsewhere yet.

Could installing Office have altered other files or fonts to cause problems? How can I fix this problem?

Any help is appreciated!