mongodb/mongo-ruby-driver — comment on commit b579a6347f41a9404ad301799eb1ca5372aee46f
File:  line 0
By gdb:

Hmm, actually, I think there are failure modes with commingling discovered nodes and seed nodes. Imagine we add and remove a (non-seed) node from the replica set. It feels surprising to me that we remember that node and keep trying to talk to it. In contrast, falling back to the original set of seed nodes is equivalent to clearing all state and starting over.

If it's useful, here was my patch for 1.3.2: https://github.com/gdb/mongo-ruby-driver/commit/003d947c22836733c36f27508ca0035f10463d98