you need to report it to the team lead/ management, so that you can make the confirmation about the validity of the requirements and then can go on with its testing. Requirements needs to match the answer for query "what customer wants?"
otherwise it could increase your testing efforts/ project delivery may get delayed/...so on and so forth....
I have the same situation lot of times, despite of following strict process. I feel this is reasonable in this competitive world.
Just get along with the functionality from BA(best case) or Dev(worst case). If the code is delivered then if tested is good. This is interesting to test from Business and User facet, will earn QA glory!
Sometimes it happens that while testing we are getting additional functionality aprart from the functionality which are mentioned in SRS.
But the main thing is that the additional functionality should not affect the other required functionality of the software.
If its not causing any problem then its just like "Buy one Get one Free"...))