The way software defects are seen on traditional vs agile projects reveals something about the differences in organizational culture. Given the following causes of defects...

Type 1: Programming error
Type 2: Misunderstood requirement
Type 3: Requirement defined incorrectly
Type 4: Discovered requirement

http://www.davenicolette.net/agile/index.blog/1590120/defects-and-culture/

Some tips about reproducting bugs - http://swreflections.blogspot.com.au/2012/08/fixing-bugs-if-you-cant-reproduce-them.html