Im not on the FS dev team, but I think you may be a little mistaken. generally your free to make modifications to open source code ( for internal use ) however its when you distribute the resultant product, then you have to make the source available.. if your only using it in-house, I dont believe your required to contribute the code back. ( however your going to end up having issues maintaining your patch set over a long period.. like can be seen here ) see here :
must be made available in Source Code form under the terms of this License either on the same media as an Executable version
if your not distributing your executable to any 3rd parties... then I dont believe you have to distribute the modified source.. Correct me if Im wrong though guys... Jay