Sorry for flogging a dead horse but not quite...   

In the new fork, nTargetTimespan is global (i.e. will be multiplied by 14 every call, and eventually overflow).  If the above snippet is original client, it is local and so will behave as expected.
Am guessing it is global now as was referenced in some other function/s, otherwise making it local would have been the better fix. 
You might want to check if mutating the value on the fly will affect any other usages of it too.

I'm assuming we are both looking at the same code, branch i0coin-0.8.x was default in git?  If not my humble apologies.