Sumantra, make sure your graph is connected. As long as your graph is connected, you should get correct result.
For this one, with arbitrary edges to make the graph connected without introducing any new cycle, I get
2-5-7-2, 2-5-8-11-7-2, and 2-5-8-14-15-11-7-2.

I think there is a bug in the grCycleBasis function. I have a large edge matrix, a part of which is:
2 5
2 7
5 8
5 7
7 11
8 11
8 14
11 15
14 15
Clearly, there are three cycles in this graph. viz. 2-5-7-2, 5-7-11-8-5 and 8-11-15-14-8. However, the function fails to recognize these three cycles individually and returns 2-5-8-7-11-2 and 2-5-8-14-15-11-7-2, completely ignoring the edges 5-7 and {5-7,8-11} respectively. It happens for several other subsets also. Please suggest a solution.
Thank you.
p.s. It calculates the number of cycles correctly though.

Comment only