I suspect that on 2008 (R2) the # is treated as a wildcard for characters that are number and this might explain why C# is handled differently by 2008 and 2012. By default SS strips leading zeros off numbers when word breaking so searching for 00123 would find documents containing 123. To get around this in 2008 you can use a custom dictionary that includes "0#" (without quotes) and then 00123 would be considered to be a word rather than a number and the leading zeros would not be stripped by the word breaker. However this behaviour has changed in 2012.

Sorry no real references to back this up, mostly by trial and error. 🙁 It would be nice if this was all documented somewhere, but I haven't been able to find much at all.